Big Problem.

[bigvariable]

Here's the problem: she won't start. My first conclusion was that there was water in the gas tank again, because about a week ago she broke down with water in the gas tanks, so I just bled the gas lines and she started right up. So this time I did that same thing, but nothing changed. I happened to break down right next to a mechanic's shop and he was kind enough to help out a little.

After ruling out water in the tank, I next concluded that it might be the starter or the spark plug. I buy a spark plug socket, but realize that the way the engine was designed, it needed the socket from the tool kit (By the way, is there anywhere I can buy the plug socket for this bike?), but I don't have one because it's an older bike that has been through a few owners. I try out the new spark plug in the line, and it got spark, so it's not the starter and the mechanic said the the manner in which it was turning over indicated that the engine isn't getting any compression. Which could mean a number of things.

My question to you is:
1) What do you think is preventing the engine from starting?
2) What would it take for me to diagnose the problem? And what would be the level of difficulty to do so?
3) How much would it cost to fix everything?

Thanks for any information you can help me with.