Create a payment website to centralize all other simple website sales

I have some websites, and each of them sell one or two products. Each one has its own shopping carts provided by a brazilian payment gateway (Pagseguro). This way I am stuck to this gateway, and cannot offer other gateways to my customers (i.e. Moip, Cielo, Paypal..). I'd like to create a shopping cart website to centralize all the sales. So when a visitor for the [login to view URL] click on "add to cart" button for the product A, the product A will be sent to the shopping cart of the website "[login to view URL]". When a user visits [login to view URL] and clicks "add to cart" button for product B, the product B will be sent to the shopping cart of website "[login to view URL]". I was researching for a ready made solution and I found out woocommerce ([login to view URL]) and wp-ecommerce ([login to view URL]). I also researched for [login to view URL] and others, but I think woocommerce and wp-ecommerce would be more suitable as they offer addons for brazilian payment gateways. After all, using with this new payment system I need to keep my affiliate system working seamlessly as it does today. I really find that it is a simple job. The only point that I cannot do for myself is the add to cart from one domain to other domain (i.e. from [login to view URL] to website [login to view URL]). Once It is done, I see no problem to deal with woocommerce or another suggested solution. My idea is to install wordpress onto site [login to view URL] and also the plugin woocommerce. And setup all "add to cart" buttons from the other sites to point to site payment.site.com.br. I really think that this is not an expensive project. I placed a range from 250 to 750 to make the project more comfortable for the developers. But I also don't know if my strategy is the best to be used.