anyone have list of flash stobes that work as slave not wire sync?

[popolarbear]

i would like to find an inexpensive stobe flash that works as slave(flashes after your cameras built in flash shoots). as mine is a cheepo and doesnt have the wire sync setup on the side. anyone have a list of slave type cameara, as i would like to study whats out there and try finding i value priced used one, perhaps on ebay, yahoo, or other used location. my budget is probably in the $50 range. also do most mounts work interchangablly or are the threads model specific... ive got an older pentax underwater that is good only for afew feet of pressure, but it takes good pictures, and im on extreame family budget but i still love this hoby.....I am sure my pictures now are limited by light quality......please any help and tips would be appreaciated. thanks