you can get spartan FPGAs for starting at around $50 however you really need to specify things like how much memory would be needed by the fifo which is related to how often the fifo is read,and how many inputs you want to be able to sample.
there are things to consider like the fact that the spartan 3 is in a bga package and requires additional power supplies at 2.5 and 1.2 volts,it would be able to handle multiple input standards with suitable switching of the i/o block voltages
I suppose as most of the design would be very similar to stuff ive already done but hasnt been used you could take what ive done and modify it to your needs.You would need to think about triggers for recording the events do you start recording immediatly or only when the inputs match some pattern? If you look at a commericail analyser you'll se there are lots of options for pattern matching before events are recorded.The other question is would it be for a commercial venture.
time wise probably not long as most of it already exists.