I needed a new derailleur on old foul weather beater bike. I bought a Shimano Tourney (lower in the hierarchy than Altus) for $12 on Amazon. It works flawlessly. It is a little ugly and heavy but I could care less. You could go up a grade or two and be very happy but maybe not necessary? Is there a bike co-op in your area. I have found beautiful used parts for next to nothing at my local co-op.