RideTech choices, need to make it happen.

[1970 TT Rustang]

Ok, right now my car is up in the air. I just removed my two rear air shocks (7000series shockwave single adjustable), due to the fact that one shock was leaking. I sent the pair out to ridetech and they told me that the one that was leaking is not rebuildable do the the age of the shock, the other shock is in working condition and is newer. So they proceed to tell me that i can get a 200 dollar credit towads new air shocks for the pair (shockwave single adjustable which are 900 without the credit).
So i start asking about coilovers, they have single adjustable pair for 650 and they will give me a 100 dollar credit for my old ones.( I like the triple adjustable, but $$$). So iam stuck now, should i just get new shockwave bags in the rear. Or do i go with the single adjustable coilovers in the rear and run shockwaves in the front (Has anyone done this? any negative benefits?). Or do i rip the hole shockwave system with the one broken shock and sell it and do coilovers all the way around.
Thanks for the help.