5K for a Thermoglass Bonham kit? It's worth a lot more than that. Heck, I'd probably give you 5K for it just to resell, especially if it has a rail mount or virgin bass drum.
However, one thing I've learned is...when someone offers you a lot of money for something, that alone can make you want to keep it more, just knowing how fast you could turn it into cash if you want to. But if you're trying to run a business buying and selling drums, never turn down a great offer. I've watched guys sit on drums for years as investments, especially wood dynas, only to see them plummet in value. Same with vintage Ringo Jazz Fests.