My #1 factor in string choice is string movement. I currently play with Beast XP and it doesn't move at all for me. However, my high school kids have copied me and they all like Beast as well. I'd like to find something a bit cheaper for them as it loses tension quick and they break strings more often than I do. I'm starting to learn to string our own racquets and id like to start stringing something consistently for all of us. So-
Best priced Synth Gut that won't move?
Best priced Poly similar to Beast that won't move?
Any Signum Pro poly - try signum pro poly plasma - the original orange one or Signum Pro Polly plasma Pure. You can get a 660' reel for under $100. I would hybrid them with a good syn gut and the strings will 1. still not move, 2. play better longer as the syn gut adds a wee bit of longevity, and 3. will play a little softer to protect the wrist, elbow and shoulder. Good syn guts: Gosen Sheep, Volkl syn gut, klip Kicker, or good ole prince syn gut w/duraflex. Get a 17G poly with a 16G syn gut. You should be able to get the cost of a hybrid stringbed down to about $4-$7 for the string.
If the kids are predominantly baseliners, have them use poly mains with syn gut crosses. If you have the rare all court player or serve and volley player; have them use syn gut mains with poly cross.
String the poly in the 46-52 range and string the syn gut 3 to 5 lbs higher than the poly as the syn gut is a softer string.