Comparing new prices to used prices is just silly...
In my area a 125 gal (72" x 18" @ 21" tall) with stand, glass tops and lights can be found for $500 USD (if you shop around)...
The 4' 150 gal is a bit of an akward size. I have a 4' x 2' x 2' 120 tal (same tank but 6" shorter) and even with my long arms reaching from the top front to the rear bottom is a long reach. The 2' front to back allowd for extensive rock/decor... but to fully utilize the 30" of height for bottom dwelling fish you really have to stack the rock/decor pretty high.
I completely admit I know next to nothing about African Cichlids, but at a glance the fish you want to stock in it looks like they would prefer more floor space and a longer tank than all that height...