If you're not interested in the .com domain name ranking, depending on your registrar and if they offer this feature, just use domain forwarding + domain masking, and point it to the other site. See what they offer, whether it be aliasing, forwarding, masking, etc. Sometimes domain registrations include features that are sometimes overlooked.

As far as being penalized, I don't see it penalizing the domain / site you've been using. (If that's the case, someone tell me so I can register a ton of domains and forward them to my competitor's sites... well, not really. I wouldn't do that).

That doesn't solve the issue of prices changing to reflect the referring domain, however. As an alternate suggestion, program the site so the prices displayed are based on the user's IP instead of the referring domain.

Otherwise, if you're interested in both domains ranking, you're best off making two unique sites (with same look, feel, and branding), so both domains would rank in their respective locations. (as incrediblehelp suggested)

__________________
Domain Name Registration and Website Hosting :: DesignerTrade