M.P.
I used to think that the bjorn was great until I learned that there are so many more COMFORTABLE & LONG TERM options out there. I was only able to use the Bjorn comfortably until my eldest daughter was about 15lbs. My youngest is now 20lbs and I still carrier her regularly in my Mei Tai's and Ring Slings.
My eyes were opened to a vast selection of baby carriers at thebabywearer.com
I have several carriers now that are so comfortable.
I use a Maya Ring Sling for short trips with my daughter and a Babyhawk, Freehand and Sachi Mei Tai carrier for longer trips.
thebabywearer.com has a great For Sale or Trade forum where you can get carriers for a less than retail.
You may spend more for an Ergo or Mei Tai than a Bjorn but you will use be able to use the Ergo or Mei Tai for so much longer than the Bjorn. I know of several people that use their Ergo well into toddlerhood. My 4 year old sometimes wants to be carried in my Mei Tai and it holds up just fine.
Good luck!