OK, buying one of those Wally Mart deals is great for spots, but not for the entire place. The consumer models are not designed to pull up a lot of the water that you will put down, meaning the carpet will take a lot of time to dry.
A rental all-in-one unit is really no better in my opinion, since it has the same problem. Let's not forget the cost of cleaning chemicals you will need...extraction fluid, stain pre-treater, gum and tar remover, rust remover, mold and mildew inhibitor, and carpet deoderizer.
You will also need time and energy to perform the operation. Time to prepare the carpet for cleaning, time to clean, and time to dry the carpet. If you are pressed for time, you will need to rent blowers to speed up the drying process or risk having your clean and still wet carpet marched on by many dirty shoes.
A big name pro will cost some major dough, but have you tried some of the smaller outfits? Mabey ask some other businesses who they use, or better yet, ask some of the cleaning companies in your area. Some of them may be like me, and do their own carpet. As a cleaning contractor, I have tried many different 'professionals' to clean my carpets at my expense and was never satisfied. A couple of years ago, I decided to purchase my own equipment so I could do a better job for my customers. My investment is about $6k for a portable machine that dries carpet in 4-8hours.
If you were to ask me to do your carpets, I would probably give you a deal if you were to have it done on a regular basis, plus mabey some free tiks! Remember, the small businessman will sympathyse more with you than the big chain will.
IMHO
The King