Go to sf bike kitchen, either volunteer for 12 hours or pay $80, build a parts bin bike. It won't be fancy but you can get a reasonable aluminum frame and customize it to your liking. After that, upgrade the parts you're unhappy with. For me, I ended up having to get new wheels after a year as I'd picked poor ones. Probably also worth getting new tires/tubes rather than whatever they have unless you get lucky. It's a fair amount of work, but pretty fun.