According to allearsnet.com the prices in 2006 were $10 for small and $12 for large. Less $5 refundable deposit. So yes it's $5 and $7. Sometimes they'll offer you a cup (or something) else in lieu of refund.
We used to get the lockers but now we usually don't. We keep our dry clothes, etc. in a beach bag at the location we pick out. And I have one of those water proof holders to wear around my neck to carry KTTW card and a little $$. This works for us. When I bring my good camera, then I usually get a locker.