It seems high to me considering the condition, there have been several on eBay recently in much better shape that went for less. (not counting that $7000 anomaly) although there won't be any shipping involved, that's worth a couple hundred right there if done right.
Knowing the CRT is good is a plus but that cabinet will have to be completely refinished, decals etc. Does it have the back & flyback cover
http://www.ebay.com/itm/VINTAGE-RCA-...p2047675.l2557
http://www.ebay.com/itm/VINTAGE-RCA-...p2047675.l2557
http://www.ebay.com/itm/RCA-621TS-B-...item27ea24dd3c
Best offer was $800 on this one:
http://www.ebay.com/itm/RCA-621TS-19...p2047675.l2557