1) A suit at or under $120 will probably be mostly or entirely synthetic. Even used, you may have trouble finding something in good shape that's wool at that price. You're gonna lose a lot of time trawling through estate and garage sales to achieve that, most likely. You don't need a super-expensive suit, but it needs to 1) fit (off-the-rack will need a tailor's hand unless you're the luckiest person in the world) and 2) not look like it's made out of nylon. If you're buying new and plan for regular wear over a long time, also consider getting a second pair of trousers with it.

2) Don't buy a black suit. It screams "I only own one suit, and it's this". It's the suit-color of CEOs who own 20 suits in many colors, and college interns who own exactly one. Navy or charcoal (a very dark grey) are much better for a business-oriented sole suit. Unless your family and friends are pretty fancy, the charcoal can probably do wedding & funeral duty, too, without getting you any funny looks. Works alright for a fancy dinner or evening event, too, unless we're talking something upscale enough that you need to be looking into dinner jackets (tuxes).

3) $120 might get you used leather shoes that are in OK shape. If you pay that much for new leather shoes, they are assuredly not leather and will fall apart in a hurry under actual wear. It'll also probably be obvious they're not real leather, especially as they wear in. Leather shoes (not boots—they're higher as there's more material) start around $200-240 new. If you're actually going to wear these shoes more than a couple times a year, go for the real thing. Used is fine, but, again, $120's pushing it on price (most of the used shoes on the market didn't start at $200ish, but more like $300+, is why most are still at or over $120 if they're in good condition)