1. Most YC founders are not college dropouts. Quite a few are in every batch of YC, but nowhere near 20%.
2. YC isn't in SF. And most YC companies don't stay in SF during YC. Lots of companies stay in Mountain View, Palo Alto, Menlo Park, etc where you can rent out a 4-6 bedroom with your co-founder(s). Housing is even cheaper in other areas like Sunnyvale, Santa Clara, and San Jose, where you can potentially have a house to yourself.
3. If you expect to get paid for starting a startup, then obviously starting a startup is not for you. By definition there's nobody there to pay you except yourself. By definition you are exchanging equity for salary.
4. YC gives you $100k: $20k directly and $80k in convertible notes (well, SAFEs now) at the best possible terms (you'd never see elsewhere). The additional value of YC is that as long as you build a product with some users, you have an extremely high chance (not guaranteed) of raising 1M+ at a 5M+ valuation. Other companies that don't raise can go on to raise more convertible notes. In fact, going through YC is one way of guaranteeing that you don't end up being offered a sucker's deal.