I just got a Hip Hammock on ebay for less than $10 shipped. It is AWESOME! I didn't know much about carriers when I registered, so I received the Baby Bjorn air carrier. I liked it, but he's SO heavy in it now (20 lbs). Jessica_anne on here (a friend IRL) suggested it and I absolutely love it.
Very easy to use, and there are lots of them on ebay still, if you're looking for something in between but not wanting to change expensive carriers at this time.
Also, be careful because some of them have been recalled. 2005 and earlier. Mine was 2006 and it's great!
Re: Rec for a cheap carrier for older babies
Isabella Faith---Born 12/17/10 via c-section.
Abigail Marie---Born 11/16/12 via c-section
BFP #3 via cancelled IUI ~ C (2lb 3oz; HELLP) 5/16/11
BFP #4 via the natural (free!) way ~ E (8lb 11oz) 9/13/12