Over the weekend I was changing a CV axle and lower ball joint. I forgot to open the master cylinder cap when pressing the brake caliper piston back in, and some fluid spilled out. When I started the car, I found out that I didn't have any brakes. I've bled them 3 times (one man bleeder kit, then gravity bled, then bled with the tube submerged in a brake fluid bottle). The brakes build pressure while the car is off, but as soon as the car turns on, the brakes go straight to the floor with little dampening. The problem is probably the master cylinder, or the brake booster. I have done the following:

1. Built up pressure with the engine off, started car, and the pedal goes to the floor (supposedly should have only depressed a few inches).
2. Started the car, held the brake pedal down and turned it off. When I release the pedal it returns immediately (supposedly shouldn't move for 30 seconds).
3. Had it inspected by a shop, and they say it's the brake booster.
4. Asked a friend who used to be Honda mechanic, and he thinks it's the master cylinder.

Obviously I don't want to fix things un-necessarily. The master cylinder runs $60, and the brake booster $110. The shop wants $270 for the master cylinder, and $320 for the brake booster.

I've replace a master cylinder before on a 91 CRX, but have never messed with the brake booster. Help!

P.S. I've searched the forums, and google.