Every time I trip over a tank at the right money I buy it..... especially the sought after alloy ones (B50MX, YZ250A/C, TM, RM A/B, CR250s), they are like real estate they are not making any more and I may need them for future projects.
I will share them amoungst my mates, but learn't the hard way twice, with people needing a tank to 'finish their dream bike' , then promptly selling it on after you give them a deal.