Well whats the price you want to buy it for? Take a bank check down with you instead…little safer that way. Then you can carry the diff in cash in case he doesnt accept. Just be like I didnt want to carry THAT much cash with me…So i got a check for $____.
You will want to contact their DMV about what is needed to get temp tags to drive it back and just contact your insurance company about what exactly to do there
edit: as far as the ATM thing…most only allow a max per day usually in the ballpark of $500