Keep the jeep and get the BMW! That's what I did. The Price on this one seems a little low for the miles that it has, but I haven't been keeping up with the market since the economy started falling so I don't know.
Make sure that you take the car to have it looked at by a qualified BMW mechanic for a prepurchase inspection. Make sure that there are up to date service records, however, buying from a used car dealer you’re probably not going to have this option. Be leery of some dealers. They will clear any CEL codes to get the car off the lot, then a few miles down the road it comes on you take it back to them and they give you the shrug and "it worked fine when we had it, sorry sold as is" statement.
Read this Wikki for some information and common problems. It's a great car and I love mine just as much as I love my Jeep too. BMW E46 - BimmerWiki