Craigslist! We ended up getting two violins, using each for about 2 years, and then selling them for more than we paid.
We rented a trumpet for a couple of months, while we figured out what to look for in a trumpet - now I'm looking for one on CL.
We bought a drum kit with bells, snare, practice pad for the equivalent of 3 months rental. Just tonight, we added a 5 piece drum set that I got for $175. If and when he moves on to need higher quality, we will sell all of these for at least as much as we paid.