Koofter

Hey guys i got a white GS 300. My tires are pretty low so just thinking of getting some rims and tires instead of replacing just the tires. Dont know much about what to get. Im interested in getting 20's any concerns? And not trying to spend too much. Would it be possible getting rims tires for about 2000. Any good sites or places anyone recomends to look at. Not sure what are the offsets or what tire sizes would fit, so any website or info would really help.
Thanks