We have a Bissell Pro-Heat and it has worked well for us. We buy them used on Craigslist or garage sales, and the ones in good condition are around $75 to $100 here. We feel it pays for itself in about 2 uses, and we keep buying the same kind each time so we learn how to fix minor things on them, and when they become unfixable (ours have lasted about 5 years) we know what to look for in a replacement. We have 4 kids, but also use them for rental properties when tenants move out and their security deposit isn't enough to pay for carpet cleaning plus all the other repairs needed.
I like the convenience of being able to use it for small spills where I otherwise wouldn't have made trips to rent a machine if my whole carpet didn't need it.
I don't buy the special solutions for them, but instead fill the little detergent dispenser part of it with straight white vinegar and it works great. (I can't speak for whether it will work in all models). I use about a quart for the whole house, so it costs me less than a dollar. I did that originally because my kids have sensitivity to fragrances in the solutions, but it also saves a lot of money.
