There is no perfect tool for this job - at least not in your price range. For long exposures though you want the steadiest you can get and that tripod isnt it.Yes but the problem is if I don't have a table or a big rock or a car or something the right hight close by the beanbag would not really help me... except if you use it in a way I am not clear on.
BTW - always shooting things from head/tripod height can get boring. For example when I photograph kids (or take photos with them in mind) I like to get down to their height.