A big factor to consider, is what your other options in your local area: how much it costs to get your racquet strung by someone, what is the lead time, how long it takes to get there, how good they are, and if they can offer strings which you like to try.
For me, personally, the big thing turned out to be stringing natural gut and natural gut based hybrids using proportional stringing method. Our local tennis shops do not offer natural gut stringing at all, and I am sure they neither would accept, nor they are qualified to do proportional stringing. Nothing less than an electronic constant pull machine with fixed clamps is up to this task. With this scenario, whatever you would save on labor, you would use for strings and more frequent restringing. In the long run, you will spend way more than you would without the machine.
If stringing with the cheapest string on the planet, synthetic gut, is your thing, than indeed you may save a bunch and can use any machine, as long as your time is worth nothing. Synthetic gut, if you buy it in reels, may cost you just about $2 or so per racquet, in materials.