I've never bought a running shirt, old t-shirts work fine, and now the races give out tech shirts it's even better.
shorts are $10 or less on clearance, socks $5 or less.
last year was the first time in 40 years I've paid over $100 for a pair of shoes, Hoka One Ones, but even those are showing up on clearance now for less than three figures.
Did run Boston in the early 90s but stayed with friends and drove up from NC, qualified at local marathons, so minimal cost there too.
It's certainly cheaper than anything else.. add green fees for golf, court fees for racketball or tennis, pool fees for swimming, on top of gear fees.. hard to show up to the golf club in a ratty old T-shirt and shorts..