That Losi you linked to is the brushless version, so no, they get cheaper.
Now the main difference you get is the brushless, of course has a brushless system. Its about the same as a 19t motor. More run time, little faster. Thats pretty much it as far as difference goes.
I now own both a XXX-S and a XXX-S brushless.
Now, thats a pretty good deal if you plan on going brushless AND not race. If you plan on racing, get the standard XXX-S and upgrade as you need. If you plan on bashing, its a good choice since brushless gives more run time, and much less maintenence than brushed motors.
Myself, I just picked up a XXX-S RTR package right here in these forums for 125.00 shipped. I might need to tear it down and clean it, maybe replace a few parts. But a heck of a deal. Plus I got a charger and batt packs to boot. Not worth anything for racing, but great basher packs.
Oh, and yes, the XXX-S smokes your choices out of the box. Another good thing about the XXX-S for bashing is it has a sealed drive train. So when you are cruising on a parking lot or a street, you wont pick up debris that can thrash your gears. I choose the XXX-S for just that reason. My local race club runs on a parking lot, and the guys with Xrays and such always have to worry about a pebble or grit in their gears getting in and messing things up.
Now, the Tamiya is also a lot of fun, I have a TL-01 I use for drifting, and they are tough cars. I ran Tamiya for years when I was a kid, bashing all around. Always easy to find parts for to. The TT-01R is a good kit, since the R means you get all the Tamiya upgrades included.
In the end, you need to decide what the car is for, bashing or racing. That will help with the choice. Plus, you point out the HPI EVO RS4, thats a nitro kit. You should decide if you want a nitro or a electric. The HPI Sprint 2 is the electric kit. And again, an open drive train.