My tread is just about done on my MTB. I am going to get some new ones but I am on a tight budget. How important is quality tread on a MTB?

Having almost no time on a mountain bike, I can't give you an answer based on any firsthand experience. But I've found endless discussions on tires with varying levels of traction and rolling resistance. Its important enough that there are entire web pages devoted to mountain bike tire reviews.

The answer probably depends on how hard you plan on riding.

Tires can in some cases be as valuable to a MTB as the frame. The right tires are key to success racing, and make it all together more enjoyable to ride on a MTB. As your tread is worn off, you don't notice the difference from when the tires were new. I recommend to buy Bontrager X3, as it is very reliable and should suit your needs.

Oh, it's only the ONLY place the bike interacts with the terrain it is passing over!

Tires are EVERYTHING. Don't skimp if you care about how well the bike climbs, corners or descends......

Very.

But what tread pattern is best is dependent on the terrain you ride.

if you ride slowly, it doesn't matter, else it's very important.

Do you mean the new one (2012 and later X3 aka 26-3, 27.5-3 or 29-3)? If so, I concur. The older Bontragers though, are junk. Here is a link to the newer one so you get the right one (their model numbering system is confusing, old and new sound similar). Bontrager: XR3 Expert (Model #11641) (they have 3 versions: comp, expert, team--in rising cost). You might not care about weight of a wire bead vs a kevlar bead but still get a great tread design and can save some $ getting a comp model.

Look Man - Sometimes yo gotta do what you gotta do - If you have to go with some cheap ChiCom tire to get out and ride then just do it...

Saw a guy ridding an old HUFFY that the only thing holding it together was its rust and a prayer - I am sure he paid more for the new WalMart tires and tubes on it then the bike - But he was ridding on a beautiful crisp day...

And he had a wonderful smile...

I like to ride xc style trails.
Bike same with generic 1.95s, rode like a bicycle not overly grippy.
Switched to 2.35 front 2.1 back, was abit nicer, more bite in the dirt for sure.
Switched to 2.4 front 2.35 rear this year, and I can feel a difference again. Moves sweet thru mud.

are you cruising down some crushed gravel trails? Then any tire will do.

Are you rolling through the wet, over woodwork, off camber, roots, steep wet rock rolls, etc? Then, time to start planning!

Tires are as important as your riding is.
I know that some bike tires can be more expensive than car tires, but it's common for you to get your money's worth when buying good quality tires.
The only thing in the pro column for cheap tires is the price.
In the con column are things like weight, traction, puncture resistance, rolling resistance, etc...

Rolling resistance is something I definatly felt when I went to wider knobbier tires. In combination with the wider gears I'm running this year seems alooooot slower and ost like I'm crawling thru some trails. Spin out really quick on the straights but climbs are butter now.