Drum Scanner - Used - Recommendations?

I am getting back into photography after several years of absence. I'm very familiar with the digital domain (developed computer graphics and 3-D software on the Silicon Graphics platform for 12 years).

I have over a thousand 4x5 chromes and B/W negatives along with hundreds of 2 1/4 x 2 1/4 images that I've taken all over the world to digitize/scan. Landscape content primarily.

Cost of having this done is obviously prohibitive SO I'll just buy a PMT drum scanner and do it myself.

I would appreciate your suggestions and guidance in defining the top one or two PMT drum scanners to consider for fine art photo.

Primary Considerations: Quality of scan - this is paramount as I plan to pursue the fine art market with large prints of unmatched quality; Ability to keep it operational - service and parts available at reasonable cost.

I have previously written SGI drivers for the Howtek drum scanner, Nikon, Sharp and the Leaf scanners and I am seeking a level of quality SUBSTANTIALLY above this level of scanners.

FYI - I have looked at Imacon 848 and found the shadow detail lacking and not meeting my needs - concluded that a true PMT scanner is essential.

Scanner will be for my personal use and not as a service bureau. Cost level I would like to keep the unit at or below is $12,000 - $15,000.

I'm seeing Isomet scanners for under $4,000 but I'm finding that parts and service are almost impossible to find. I'm also considering a refurb'd ICG 350.

Your guidance and experience are sincerely appreciated.
Thanks