Magento work: Multiple sites with different languages and same admin for all sites

We have chosen Magento as engine for the new version of our webshop. One of the strengths of Magento is the ability to run multiple stores from the same admin. Our concept will be that we will have one shop for each market: Poland, sweden, Denmark etc and each shop will then have their respective language installed. In backend we would like to be able to manage our sites easily with each language. What I mean is that we eg would like to be able to upload a product and make a different price from each market, so that the polish site has different price, description title etc (all data) than the Danish site. So it will be like this: Danish site - Danish language Polish site - polish language Etc But all these sites will be managed from one admin. Check this link as reference: [login to view URL] We would like to stay true to the core of magento, and we only want changes in the core that will remain when we Update the software. It is very important that this kind of setup is made mostly in the admin panel and with changes in backend that will be functional once the software gets updated. Please give us a price on this setup.