i'm so sorry for your loss. grandmas are very special.
it is a pretty machine - outside of addicts there isn't too much of a market for treadles, so it just depends on if you find the right person. looking at your machine, it will need a new belt and a good cleaning. the chrome parts are pretty dirty, but some chrome polish and work would clean them up. the working parts probably need cleaning & oiling and lubricant.
the cabinet is beautiful. lots of detailing on the drawers that appeals to people and the wood looks in good shape.
how much people will pay for it varies a lot from region to region. around here (oregon) treadles are anywhere from $15 on up, depending on condition and whether or not there are attachments. If you want to sell it as is, on craigslist for example, probably something around $25-60ish, maybe? i'm thinking in Montana you might have lots of them floating around. You might check online and see what the going prices are. sell locally - you don't want to ship it. they are too fragile and expensive to ship.
Brandon, i'm guessing you might be youngish - someday you might really treasure your grandma's sewing machine. our tastes change as we go through life, and you might have a wife/daughter or you who ends up appreciating antiques, especially a family piece. I might be completely off-base, so ignore me if so, but you're not going to see a lot of money from this unless you put some work into cleaning it up. it might be worth more to you as a reminder of your grandma. My grandma died when i was 23 and i have her treadle and her pump organ. Never "use" either one of them but every time i look at them i smile and remember her. just wanted to throw it out there in case you hadn't considered that.