You can still sell ads via the Transfer function, it's just annoying and slightly more risky (preferably deal with someone trustworthy, or make them give you the stuff before you give to them - and take plenty of screenies).
750k is kind of the ideal price to buy them for; if you're selling them, you may try to sell for more than 750k, such as 800k. I might buy a few ads at that price, but for very many ads I won't buy unless they're at 750k and I think most other people feel the same way. If you're trying to sell fast to make a quick buck, you might try selling them for under 750k, but even 750k should sell pretty fast.
