The biggest problem with film scanning is not the hardware but the time that it takes. Fiddling with colour correction, dust removal, grain reduction and sharpening all add to the time taken. (Some of this can be fun, and part of the game, but still it can still chew up much more time than deserved.)
If you get a not-so-great film scanner, you could end up disappointed by the results, get a better scanner, and do much of your scanning again.
So, if you're already sure that you want to get into scanning, I'd suggest increasing the budget, and "doing it right" -- e.g. with a Nikon V.
You can probably add a decent document scanner for around $40 if needed.
In any case, and esp. if you're not sure, you should be able to find many used film-capable scanners. At the low end, you might try to get a used Epson 2450 or 3000-something to get you started, and see if you can stand the time commitment and if the results are good enough for your usage -- this could also serve as your cheap document scanner, as mine currently does.
One notable problem with the 2450 and other cheap/old scanners is a lack of digital ICE -- this is very helpful for saving time.