Free: Contests & Raffles.
I bought a 555 block two weekends ago for $26 at Dicks.Sportsmanship had CCI, in 100s for $18 and cheap 50s for $4-6.It depends on where you go and when you are there. So far, I have not paid over $35 for 500--even last year. Of course, I went to Montana that year and bought several bricks on the road. My 22s are not picky about the type of shell, so cheap works for plinking.
.22 Rimfire has been available from the beginning of time if your willing to pay for it.