I used to live in Lindenwood almost Rockwood park, know what you mean bout
cheaper than Manhattan.
okay, I'm not going to repeat what everyone else said but add a few things.
There is nothing like the feeling of climbing on a bike that you built up yourself.
it's that proud feeling you got when you were a kid and completed your first
model car/plane/ship only better.
Once you do that, there are few mechanicals that are going to sideline you,
or that you can't either fix or replace. Now I'm not saying that screwing in
a bottom bracket will make you automagically able to fix broken derailleurs,
but you will be more willing to tackle it rather than drag the bike to the LBS
or let it moulder in the garage (or downstairs storage bin as the case may be).
now before you do much else, go to a decent used book store ( manhattan I'm
thinking) and find an 80s to 90s version of either the Zinn book
Zinn and the Art of Bicycle Maintenance or the Bicycling versions
of the same Bicycling guide to Bike maintenance. the modern books
won't cover friction shifting, non aero cables etc.

then ask questions here and have fun.

Marty