I agree with Curtis that you really need to be paying $1-2K for a half decent copywriter. It is definitely possible to find good copywriters in RAC and Guru but it can be difficult. If you ask who they have written sales letters before they will probably have signed NDAs so can't tell you!

Again to agree with Curtis, make sure you go for a native English speaker, your sales letter is arguably the most important piece of work in your project so you can't afford to make a bad decision.

Alan