Most step through mopeds have a height adjustable seat, obvious exceptions that come to mind are any with a longer/2 person seat, like the Honda Hobbit. The rest of the proportions might be a little tight though. Magnums are suited for taller people but expensive. I have a 2003 Sachs from Europe that is a step through but surprisingly tall, like I can't put both my feet flat on the ground when riding it even though I can touch the ground fine on my cb550.
Price wise, markets vary. But consider that there are $300 stock maxis that pop up all the time all over the country, and that shipping would be around $200 depending on where you are and where the bike is. A Maxi that has new tires, brakes, cables, but stock motor is worth ~$450 all day. A bone stock Maxi with a motor rebuilt by someone competent is worth around $600.
Point is, don't pay a grand for a Maxi. Avoid Tampa Steve, dude has fucked over enough people to warrant not doing business with him, and he doesn't know jack shit about working on bikes