I'm of course a bit biased but I will still give you an honest answer
ThePaysiteCMS while a good product by good people but it is out of your indicated price range.
Sitedepth and awiz are decent products if you want to keep things simple. They will do the basics and are priced lower. If you want to really customize your members area and have total flexibility you need a different product tho.
That leaves CARMA, MAS, and ElevatedX.
I have seen some good feedback about MAS from Mansion clients however the demos I have seen of it do not put it at the level of CARMA and ElevatedX. It is a good solution if you also want to pay a monthly fee for an outsourced employee to build and maintain your members area with the software as Mansion provides this service as far as I am aware.
Now we're down to CARMA and ElevatedX. IMO they are the two products out of the list that sit at the top. I believe CARMA can be a bit more flexible with allowing you to design your members area EXACTLY as you wish however that creates a larger learning curve and more involvement on your part of on the part of the integrator. I think ElevatedX is a bit more polished and carries a few native features which CARMA does not.
We have spent a lot of time the past year plus with NATS v4 and now that is starting to roll out (smoothly!) with the second phase of beta starting this week. Once mass upgrades are started to NATS v4 we are beginning a major rewrite of CARMA to CARMA v2.0. I will make sure as I did with NATS v4 that CARMA v2 is WAY ahead of any other solution. However, CARMA v2 is going to be at least 3-4 months away I would say.
As you are a NATS user now you should also have a cleaner integration with CARMA (v1 and v2).
Both CARMA and ElevatedX are great products and I believe you will be happy with either one.
The bottom line I guess is you will put more work in with CARMA but you have total flexibility as well as the opportunity to participate in the reworking of CARMA v2.