I certainly would have interest in some products to help support Larian in developing future games. Here are some of the things that I would definatelty purchase and what I consider a fair price in US dollars:

Coffee Mug: $10 - $15 (maybe with the picture of Samuel standing outside his Citadel on the mug)

A Jewel Case: $10 (that will hold Divine Divinity, Beyond Divinity, & Divinity 2 CDs. And the Larian Games Logo on the case)

A Book of DD and BD area maps: $10 - $15 ($20 if it includes a signed picture of the development team)

A chair that does not make my bum sore after 12 hours of playing: (price negotiable)

I think these items would be rather cheap for Larian to have made (except the chair), and could bring them a few extra coins to keep the great RPGs coming.