I would consider ordering an Epson 3170 online. These are decent scanners
for the money - especially considering your budget. Amazon often has promos
on these scanners. They may be replaced by a newer model soon, so you can
find some decent deals on them. Epson announced a few new scanners but I
think the medium format one will be over $200 US and it won't be out until
mid August if I remember right.
You will have to make a compromise since you need both 35 mm and medium
format capabilities. A dedicated film scanner would do better with 35 mm
but considering your budget and needs, I would look at the Epson 3170.
Unless you can find a deal on something used, you are going to have to
budget quite a bit more before you will get anything that is a significant
step up.
My $.02,
Doug