vacuum advice for carpet + hardwood, especially dust on carpet

My home is about 50/50 carpet/hardwood (although I'm hoping to replace most of the carpet with hardwood and rugs in the next few years). I have a roomba, but I want another vacuum that can really get up dirt/dust, especially since I have bad dust mite allergies with the carpet. I was hoping for a vacuum around $200, but I would go as far as $450 if that would make a big difference in getting the job done. Any suggestions would be very helpful!