To be more specific, for a software piece that goes for around ~ 300$ - the salesletter and adwords text and followup emails ? Does the rate depend on the product price?
It doesn't depend on the price of the product. It depends on the writers time, skill and abilities. I think the price would be anywhere from $500 to $1000 depending on the experience of the writer and also how many sales letters you desire ( two is recommended for testing) and also how many emails you want as well. Good Luck!
if the price about $500-$1000, how about the ROI? let's said the writer have high experience and i paid him/her $1000. how much the percentage of ROI that i could get?