You can still get a good price on a Shimano R700 Compact
. This includes the BB, it's sold by a brick & mortar dealer, and it will function just as well as the 6750.
Changing cranks will require a special tool to remove/install the BB, but the same tool will work on both. You'll also need a couple of allen keys (or, ideally, allen socket heads), some grease, and some common sense so you don't crossthread the bottom bracket shell. You can go to parktool.com, sheldonbrown.com, or check out a good repair manual from the library if available. If you don't want to buy the tool(s) or have doubts about doing the job, your lbs can do it.