Quite a tight budget if you're looking to live on your own! Very little if anything in the city for that, unless you're willing to go into a shared house. Good or bad areas, although TBH Cambridge doesn't have proper bad areas if you're used to larger cities.
The rental market can be pretty vicious, even outside of Cambridge. Properties having lots of viewings and going quickly, high fees etc.
The Research park isn't actually that close to Waterbeach, which is a problem for e.g. train.
You can consider cycling: it's common for commuting around here. Cottenham, Milton, Landbeach, Histon, Impington are all close enough to cycle, though the conditions aren't great. I believe there is a 'back access' to the Research Park by bridleway, which avoids the A10. Otherwise there's an okay cycling route via Landbeach, but can't avoid the last small section on the A10. There is no pavement here either, so walking is out.
I don't know so much about driving to Waterbeach, but don't assume car is the pain-free option. The traffic around here is awful, the A14 grinds to a halt regularly, depending on where you are. But the location of Research Park may limit other options. If you do commute by car, it's still not the best way to travel into Cambridge due to congestion and lack of parking.
Don't know about the buses, sorry. They certainly don't go into the evenings, so you might be restricted on times.
Histon and Impington are on the Guided Busway, which means getting to Cambridge by bus, walking or cycling is very easy. Heading further north, Oakington, Longstanton, Over etc also on the busway, with several other villages not far off.