Totally agree. Buying them from a restaurant supply store (here in the midwest we have Gordon's Food Supply, or GFS for short), I pay about 6 cents/each for 8oz and 8 cents/each for 16oz and every two weeks I throw them out and put new ones in. That way I don't have to worry about washing them and having detergents left in the dish that could be harmful to the animals. Well worth the $7/week in my opinion.
Just setting the water bowl in a cage will almost certainly lead to spillage. There are a few methods you can do to prevent this. In my smaller snakes, I glue (non toxic glue) a water bowl down to the tub, then set the actual water bowl itself down in it. For my larger snakes, I have to use a water crock (both SuperPet and Ethical Pet Products make a 5" water bowl that holds them perfectly...they run about $4-5 each. Another way to do it is to find a PVC pipe that is the right dimension (I'm guessing that would be a 5" pipe but I can't be for sure) then cut slices off a few inches high. You set that down in your cage and then set the bowl in that.
Good luck,
Jason @ Jason's Jungle