That's a good price!
Check the yardage price for the carpet. $36.95/yd.
It takes 4.5 yards to do the carpets from scratch. That works out to about $175.00. JUST for the carpet! Plus underlay! $15.00/yd. 3.5 yards needed. Better than another $50.00! $225.00 in materials, +tax, +shipping, before labor!
So, that $121.95 is actually a smokin' deal! Almost 1/2 the price of the raw materials!
I hardly ever make carpet sets anymore. Easier just to order some up!
If you don't want the heal pad, that becomes a special order. Be prepared to wait. & wait!
Don't know if this Co. will do that, but I've bought carpets from ACC, & they do, but it was more than a 6 week wait. And just a general hassle to even get them ordered.
That Co. has the option of having the underlay sent as separate from the carpets. Adds a step to the install, but I find that the carpets will fit better. Most carpet kits that I install, get the underlay pulled off the carpet & installed separately anyhow. With the underlay pre-attached, the carpet doesn't want to stretch & form as well as it does by doing the underlay install as a separate step
Not familiar with that 'Mass Backing'. Seems like a good idea. You could probably get the same effect from a good layer of deadener. But you're not gonna do the whole floor in deadener for $54.00!