I bought a RRA Tactical CAR A4 back before the ban ended, and ended up evilifying it until I pretty much had the Government Model. The stock rifle was about $835 or so. Let's do a little math shall we?
(Some of these prices were government discounts, but you could probably do better with a little shopping around on the EE.)
Eotech 552 - $335 or so
Arms #40L flipup BUIS - $100 (this one is more compact than whatever they have on there, and more expensive than the standard #40
Surefire M73 Quad Rail - $200
I bought a Surefire G2 and an Vltor scout mount for my lighting needs along with a VFG, but let's just say you wanted to buy the M951 light they have on there. On Surefire's website the better model runs for $445. Add $50 or so for a chrome lined barrel on the Tactical CAR A4 (which mine doesn't have), and you're hitting $1965 for what you see there.
That leaves you some money to buy some nifty extras like more mags, a VFG, or a better stock than the one they have on there. (I bought an LMT SOPMOD, and it's ridiculously comfortable to shoot and is rock solid.)
Of course, sometimes it's worth the premium to have everything put on there right the first time, and not have to wait for all the pieces. It's up to you.
It's a great gun, whatever you decide. My RRA has had zero problems for me.
Anyway, now you have some quantification.
hnot flush with the top rail of the receiver, which may cause you issues depending on how you want your sighting gear set up. If you wanted to mount an EOTech with one of those nifty magnifier thingies in front of it that I've been hearing about lately, you may run into difficulties.