I'm not a expert on this but look at it this way. 1000 hours on a 10 or so year old tractor (diesel) isn't many. Is a manual available with the purchase, does it run? Did you see everything working.........
Many people will say the lack of a used book to gauge a purchase is a problem but sense nothing really exists then you need to make an educated guess.
EBay has some 5100 for sale for more than 3k. Yours has some nice working attachments and it's 4wd, diesel. To buy something new today would be 10,000 for the same set up.
My comment to you would be to shop around and see what 3000 can get you vs the
B5100. It doesn't sound unreasonale to ask for 3000 anyway.