I am a fast progressing player, athletic, late 40s, and at an approximate high 3.0, low 3.5 level. I expect to be very solid 3.5 in about six months, even 4.0 in about 18.
I value control, precision, and can generate my own power. I like to hit topspin but in moderation. I also like to flatten my shots, and to send slices. I would consider myself an all around player with a 1HBH.
I've been having elbow and some shoulder pain from bad serving and backhand technique which I since corrected, but pain can still come back easily if I play twice a day, or with a stiffer frame and a string.
I play and intend to play with Wilson Blade 98 16x19 for a long time. I love it for its feel, control, and how it is on a serve. I currently have Solinco Hyper G in it at 52 lbs. I like the spin HG gives, but I feel I might need a string with more comfort, good control, and a tad bit more power.
Currently, Hyper G is doing good for me, but it is probably also a little bit underpowered, and too stiff for my joints. I also feel that Blade could take a bit more power than what Hyper G can provide.
I have been considering full bed Triax, or Wilson Synthetic Gut Power. I am not yet at the point where I am into hybrids, or can re-string racquet every two weeks. In fact, Hyper G lasts me 2-3 months of moderate 3-4 times a week play. I would however consider a good hybrid, if you have something to recommend.
Do you have an affordable ($5-$20), durable, comfortable, precision-oriented string to recommend (full bed or hybrid)?
As I said, I've been looking into either high-end synthetic gut, or a string like Triax (based on reviews).
First of all, welcome to Tennis Warehouse's Talk Tennis forum. This forum is comprised of players ranging from 5.5 to beginners. Some are teaching pros, some are professional stringers. There are lots of good people on this forum.
my .02 on your initial post: You're a beginner playing with Hyper G and now you have both elbow and shoulder pain from hitting with a string not designed for 90% of rec players.
Whoever strung your frame did you a great disservice. 
That's a different topic completely.
1)
Lose the poly completely. Not poly whatsoever. If you want to have a cool looking green string in your frame, Wilson makes a multifilament called Sensation in green. If you want it to be more color-coordinated, grab some 1.30mm black Head Velocity for your mains, and use green Wilson Sensation. If care more about the performance of your strings rather than the strings matching your frame, put a full bed of $10 a pack Head Velocity 1.30mm in your frame. If you want the best multifilament company's top of the line, multi, put some Tecnfibre X1-Biphase 1.30mm in a full bed. If you want a better setup for $15, go with X1 Mains and Head Velocity Crosses. When you break 1,30mm X1 or Velocity mains in less than 16 hours, I can give you other suggestions. Not a fan of Sensation at all, but yes, I do stock in both Natural and Green reels for those players that require color coordination after Hyper G gives them tennis elbow. That's not a joke, unfortunately.
Despite your self-assessment, you are in fact a beginning player, not a 4.0, not even a 3.5 player. This isn't a slam on you in any manner, it's just a fact. Therefore poly isn't going to help your game whatsoever right now, and will only continue to hurt your body. You can choose to ignore this fact or keep playing with poly and injury your elbow and shoulder to a point you might need surgery. There is no reason for you to even be using a hybrid with poly until your elbow and shoulder are both better, then and only then should you start with a hybrid of something like Velocity mains / Cream crosses.
2) Lower your expectations of becoming a 4.0 in 18 months and seek the skills of a 4.0 player, not a rating. Ratings come out in Dec of each year, and this year nobody is getting bumped up or down due to Covid, so perhaps adjust your goals to a yearly goal. There are no 18-month bump ups/downs. Many players have your line of thoughts and expectations to advance to a rating quickly.
A better goal might be to win a few 3.0 tournaments, then play in some 3.5 tournaments and see if you can advance deep and win a 3.5 tournament. That's a goal you can achieve as you enter more tournaments, rather than waiting for Dec 2021 to see if the USTA bumps you up. If you are playing tournaments and doing well, you will have a clear indication of your progression.
Here's the deal. You are a rec player in your late 40s. You're not a 12-year-old junior taking lessons from an Elite Academy four hours each day. Very few players in the US advance from a beginner in their late 30s to 4.0 in 24 months. That's likely for an ex collegiate baseball player, but unless you played a collegiate sport like baseball, basketball, or hockey, it's just an unrealistic timeline and puts a lot of pressure on yourself. Can you do it? Maybe if it was 2017 and you had two years to go from 3.0 to 4.0, but you are putting a lot of pressure on yourself. In 2021 you will still be a 3.0S or 3.0C as the USTA isn't bumping anyone up or down. My .02 is to try playing in 3.5 tournaments until you win them. There will be plenty of 3.5 players seeking to move up just like you and you are likely to find good competition.
3)
Forget the one-handed backhand (OHBH) and learned to hit a two-handed backhand.(THBH) Honestly, a OHBH is the one-shot, 95% of 4.0 players don't have. When I see a 4.0 with a one-handed backhand, I attack it relentlessly, because 90% of 4.0 players with an OHBH can't hurt a 3.5 with their OHBH, an 95% of them can't hurt another 4.0 with their OHBH. 4.0 men with THBHs can hurt other 4.0 men with their 2HBHs. Sure these 4.0 players have visions of Stan the Man and Fed in their heads, but honestly, at 4.0, most players are hacks, including myself. A relentless hack, but still a hack who enjoys tennis as a way to get some calories burned and hang out with friends on a tennis court.
My advice: Enjoy tennis, your friends, and take lessons from a good teaching pro, ditch the poly and learn to hit a 2HBH. You're welcome.
To the other TW TT readers: Remember me writing the number of players with a
Wilson Blade 98 with Hyper G has reached pandemic levels in Charleston and Mount Pleasant SC? Here is yet another poster who admits it.

His club did him a major disservice.