Originally Posted by cnnrmccloskey

its a 20 speed? do you mean a 21 speed, 20 is only possible with a 10 speed cassette. if you mean 21 that means you have a triple and will probably have to get a new BB.
I don't have any budget suggestions other than avoid spending too much money until you know you like FG riding and you want to continue.

before we go further. Does your bike have horizontal dropouts?