I got mine at Lowe's, so you might check there if you have one in your area (I bought it online and picked it up free at the store.)
The Hoover is heavier b/c of the (I'm assuming) massive suction machinery in it and then, of course, you have to add water. I have a dog and a cat that both shed like mad, so even w/regular vacuuming the Hoover sucks up a lot of ground-in hair, so getting the Hoover clean after using it involves getting down on the floor w/Q-Tips to get the area around the brushes free of all fur.
I didn't buy mine from Amazon, but the reviews there were helpful:
http://www.amazon.com/Hoover-MaxExtract-Carpet-Cleaner-F7412900/dp/B0013YPWE6/ref=sr_1_1?ie=UTF8&qid=1369917726&sr=8-1&keywords=hoover+dual+v+steamvac (This is a newer version of what I have with some nice updates like automatic rinsing)
One final tip: Once the carpets are clean, run the Hoover over them "dry" (i.e. just the suction on, not adding any water) This gets the carpet almost 100% dry and they fully dry w/in an hour, not the many hours it takes with those rent-from-the-store machines.
If aren't dealing with pets (and I also live on a dirt road for extra filth!) and you have health concerns, hiring professional steam cleaners to get the carpets back to decent shape and then maintaining w/the Shark might be the way to go.
Good luck! Let us know what you decide.