Cat liter smell

HELP PLEASE!!!!!
   
We have 2 cats and a small apartment. We are also on a very tight budget.
   
We have tried several different ways to keep the cat box smell to as little as possible. It is expensive and time consuming. Every method seems to have its drawbacks.
   
What is the least expensive way to keep the cat box from smelling?
   
Our cat's seem very good at excepting cat food and litter changes. We would like to get them on a system that works well for them but doesn't cost so much.

The "worlds best cat litter" made of corn works incredibly well at keeping odors at bay, but its a little pricier than some other types.
   
It's also flush-able, so if you happen to have the catbox in the bathroom like a lot of people do, you could scoop multiple times a day and just flush without much inconvenience...
   

I use the pine-pellet litter. 1 1/2 inches of litter for 2 cats lasts 24 hours. ExquisiCat is cheaper than Feline Pine ($8.99 for 25 lbs at Petsmart). The stuff works beautifully.
   
You can tell when the litter is all used up because all of it fluffs up into sawdust.