I bought a 99 WS6 a couple months ago for $22k. I raced an M5, and was basically even with that up to 75. Beat my friend's 97 automatic TT Supra with an air intake and 3.74" exhaust and I was bone stock down to the Fram filter. It is the fastest car in it's price range, handling is very crisp for stock, and it comes with many comforts like standard leather, t-tops, lumbar seats, 500 watt 10 speaker system. You can call the interior cheap, but I think that's not true and have seen too many imports and other domestics with very similar plastic stuff. The LS1 motor is VERY reliable, handles power boosters very well, all aluminum block and heads, hypereutectic pistons. It is just a very well engineered car. The WS6 package can be put on the Formula OR the Trans Am, but I chose the TA b/c it has factory front brake coolers. And the WS6 package adds the ram-air hood, freer exhaust, stiffer springs, shocks, sway bars, and 17" rims. Not to mention I get 30 mpg on the highway and 21 around town!!
Again, just my opinion. I think I've driven every other car that was mentioned previously--TT Supra's, Type R's, 92-96 LT1/LT4 vettes. The only car as fast as the LS1 WS6/SS would be the LT4. The LT1 vette, TT, and Type R aren't as fast. And you'd be hard pressed to find a quality LT4 for $20k--definitely not a collector's edition or GS.
It all depends on what you want I guess.
------------------
99 Trans Am WS.6
89 Camaro RS
76 Corvette
66 Chevelle Malibu