Red ear slider turtle. Need help.

[Beardedragon]

how much do water filters cost?

The cheaper they are the less they will work and the more your turtle tank will smell( badly). The best kind to get for turtles is a Canister filter, which run at around $120. Another type is a internal which are cheaper and do not work nearly as well.

Id get a Rena FilStar xP3 Canister Filter, which filter 350 gph.

For any tank you have you want the filter to be twice as powerful, so the rena is good up to a 175 gallon tank and keeps them spotless between weekly water changes.