Good Source for filters

Do you need to use colored filters with digital camera? You can always add the effect in post processing.

I doubt you will find a screw on 58mm filter for $20 but there is a system that uses square filters with a holder. "Cokin" is the brand. You will have to buy a holder and a 58mm adaptor ring but after then the filters are cheap, under $20, I think. One advantage of square is that you can get gradient filters that are darker on one side. See URL below. There are sold "everywhere" Try B&H or Amazon

http://www.cokin.co.uk/pages/main.htm

 

Cokin is your better bet because you really do get what you pay for in filters.
However....I would certainly try this badboy from ritz camera.
Tobacco Filter $19.99 but it is cokin.