If you want to spend copious amounts of money in Mammoth you certainly can. I’ve written previously about how expensive (and white) snow sports are. And even if you have the cash to blow, I’m a fan of blowing it where I want to, rather than being forced to out of circumstance.
A single night at the Westin in Mammoth Village will set you back over $700 in peak season. Conversely you can be at the EdelWeiss’ Studio for $100 night. Is the Westin vastly “better”? Of course it is. But for my bank account I’d rather pocket the $600 difference and buy a top of the line snowboard with it. Again: let me save money where I like so I spend it where I like.
So here are some ways you can spend (relatively) less money visiting Mammoth:

You might see two hostel names floating around, but Holiday Hause and Moderne Hostel are the same thing (both at 3905 Main St). Regardless, you can stay in a hostel setting for $41/night. Having stayed in hostels before I actually kind of dig it because you meet new people and can frequently tag along with others for night life.
Note also that the Mammoth hostel also has a kitchen which is where you can save real bucks. Vons is by far the largest (and really the only) grocery store in Mammoth. The prices tend to be a bit higher even before the 1% tourism fee is applied to everything, so consider getting your groceries in advance. Either way, try hard to have your breakfast and dinner prepared in the hostel kitchen.
Stealing from my article on how to save money snowboarding, tuck some lunch in your backpack before you head up to the mountain. One place it’s hard to not spend some money is at the lodge buying a beer at the end of the day. But you can bypass that one too by tucking an IPA into your bag, and nestling it in the snow in a treewell somewhere (make sure to put it on the downhill side of the tree so no one follows your track and nails it).
For lift tickets, the best I’ve found is Costco’s deal of 4 tickets for $300 (this comes and goes by the month). Also consider that with 4 lessons you can frequently get a season pass: something to consider.
But with the Costco deal, staying in a hotel, and $20/day for food you can shred the mountain for $41 (lodging) + $20 (food) + $75 (lift) = $136/day. A four day amazing trip would run the tab to $544. Still less than a single night at the Westin, I might add.