Costs for leased lines from the states to either Linx, Ams-Ix or DE-Cix are all more or less the same. You should chose the ixp from you can benefit most. DE-Cix has done a lot in the past few months to attract more members from eastern Europe. Because of its position just in the middle of Europe you should have the best coverage to western as well as eastern Europe.
A short comparison: Exchange / Traffic on public exchange vlan / Number of members LINX: ~ 77 Gbps / 210 members AMS-IX: ???* Gbps / 244 members DE-CIX: 51 Gbps / 184 members * = the webpage says about 110 Gbps but as far as I know a lot of Dutch isps are carrying some sort of mirror-traffic over the ams-ix because of legal monitoring reasons (correct me if I'm wrong) If you ask me then AMS-IX and LINX are both very good exchanges. The de-cix is a little bit smaller but has a lot of potential due to eastern Europe isps joining more and more. Gunther