I'm sorry, I meant to say that bypasses the digestive system, not the brain, which is of course where the GABA needs to go. It does this because GABA isn't digested very well as a supplement by itself, as it doesn't often make it to where you need it most.
It won't be as strong, obviously. Your body uses taurine and B6 plus other cofactors to manufacture GABA, but gabapentin is pure GABA that bypasses the brain. Sometimes you can get a doctor to continue to refill prescriptions even if you can't afford to see him or her anymore, and there are community health clinics for people who can't afford healthcare. There are other ways to attack pain, of course, but the methods would depend on why you have the pain.