Title. I know the guy in dragonsreach will buy staves, but he has like..9 gold.

Try general merchants and the court wizards.

College of Winterhold. or find other Court Wizards in other cities. Or try the Riverwood Trader and other general merchants.

Anyone who sells magic supplies will buy staffs, so if one guy is out of money just visit another; as it takes more than two game-days to visit more than about 4 Hold capitals, there should always be somebody with enough cash to buy at least 1-2 of them each time. IIRC, all merchants at the College (which is all the master mages, who are also all trainers) will buy them, except possibly the guy in charge of the Arcaneum since he's strictly a bookseller.

If you actually perk Speech, which few people do, then the Merchant perk will let you sell anything to anyone save for stolen goods, which require the Fence perk from Speech if you're not working for the Thieves' Guild.