Like most things..you just have to prioritize what you spend your money on.

I spent good money on a quality lock, pump/mini-pump, multi-tool. I learned how basic maintenance + how to change a flat.

Also, I'd recommend a quality bike after you've ridden a few cheap ones..It's very easy to spend <$100 on an 80's-early 90's mountain bike (in fact I bought one for $40 yesterday w/ rack+basket) and commute on that. Even if you spend another $100 for new tires/tubes + tune-up..that's a great commuting bike for under $200..Any quality accessories you get should be transferable to any future bikes..so the cost should be negligible over time.

If later it turns out you think you'd like to tour or do brevets or race..you can buy a nice quality bike specific to that..transfer most of the accessories..(even sell that mtb; although i'd keep it).

You can spend a fortune on most anything..for example: a flat can be fixed with a patch kit (<$1) or a new tube (<$5). If your tires are worn..i suspect that you've done enough riding to have "earned" a nice new pair of tires.

I bought one of those child seats for the bike..paid $110 for it...in hindsight i should have bought one used since they are plentiful and usually in very good condition--(at least here in nyc)..When my daughter had outgrown it...I took the opportunity to sell it + my first bike (used hybrid $140)..for about $160. Overall, i spent +$90..rode the hybrid +1500 miles, lost about 10#, my kid enjoyed countless rides to the park and beach AND..in the meantime I learned that I preferred being on a road bike. That seems like a steal for under $100.

I've had my last road bike for 2000+ miles. ($100 mid-80's vintage japanese bike) ..I've since bought a child seat..used $40..and my daughter and son will get plenty out of it.