Digitalriver,ebay,TTZ media.Shopzilla is some name you can try and study and play your luck with

I think that should be cost around $200 the practice of all that kind seo actions is quite basic need of SEO so most SEO new can do that,to be advanced it need long tail analytic and implementation...

for me my best marketing effort is trough combination blogging and adwords with additional longtail research,it is basically marketing base on community gathering,creating place so that people love...