When is enough enough?

When do you decide enough is enough and quit trying (ie. testing, measuring)?  My DH and I have been trying for our first for a year and a half. We saw a fertility specialist and they said that we should start looking into IVF but we can't afford it and our ins doesn't cover it. I was hoping more rigourous checking would help but now I'm ready to just say forget it and quit all of it. And if we get a BFP great. Thoughts?