I don't think a list of this has been done yet. No prototypes but "special releases" do count. All regions are a go. PAL NTSC or JAP its all good for this list.
1. Kizuna Encounter Neo Geo European Test Cartridge ($8,000)
2. 2600 Air Raid complete ($4,000)
NES NWC gold cart ($4,000)
Ultimate 11 Neo Geo (Super Sidekicks 4) ($4,000)
5. Video Life complete ($3,000)
6. Metal Slug Neo Geo ($2,500)
7. 2600 Ultravision Karate complete ($2,000)
2600 Gauntlet complete ($2,000)
9. Quiz Chibi Deluxe Neo Geo Japanese ($1,800)
10. NES NWC grey $1,500
2600 Eli's Ladder complete $1,500
2005 update (so far)
1. Kizuna Encounter Neo Geo European Test Cartridge ($8,000)
2. NES NWC gold cart ($5,000)
3. Ultimate 11 Neo Geo (Super Sidekicks 4) ($4,000)
4. NES NWC grey $3,500
5. 2600 Video Life complete ($3,000)
6. Metal Slug Neo Geo ($2,500)
7. 2600 Ultravision Karate complete ($2,000)
2600 Gauntlet complete ($2,000)
9. Eli's Ladder complete $2,000)
10. Quiz Chibi Deluxe Neo Geo Japanese ($1,800)