Buick Regal T-type/Grand National option packages have better road suspensions than the '87 Monte SS's did. HD sway bars and spring/shock combos came stock on these cars. There are two GN's in the driveway, they were identical in terms of suspensions till one was modded for drag only (it has the capability to run mid 10's and then drive home), while the other is more of a daily driver. Dispite a "lumpy" cam, bigger 43lb/hr injectors, a Thrasher chip and a slightly larger turbo, it's still very driveable and can take a corner almost as good as my '94 Firebird Formula LT1/T56/3.42 rear (which handles/rides better than it's no-frills brother, my fathers '94 Camaro Z28 LT1/4L60E/2.73 rear.
The advatage of owning a GN, aside from being able to destroy just about any import that doesn't show up on a trailer, and still have the A/C on, is that insurance counts this "vette killer" as an ordinary non-turbo'd 3.8L Regal... Cheaper insurance! And if you were to throw a few grand into the suspension/wheel/tire category, you'd end up being able to pass porsches round a corner on the outside.
Call me bias, but an upgraded '86/'87 GN will have the edge against an Audi A4, 3 series, or C class (notably driven by ricks), and in my book outclasses them because Buick is GM's mid class fleet. Even if you dump $5G into the car to make it fast(er) and handle corners like a G-machine you can still stay within your budget of $15G. A "nice" GN will go for about $5G-$10G, the GNX variant being a low production version and considered a collectable (>2000 made) will be in the $20G-$30G range, while the Regal T-type cousin (available in a few more hues than black) will go from about $2G-$6G depending on the condition and mods already done (which it's a rarety to catch a GN/T-type bone stock anymore).
The stock block can push the 3800+lb car into the mid to low 11's in the quarter mile. (that's roughly 500-600RWHP) While you can drive it daily, hold 4 track tires and four of your buddies/chicks while paying insurance on a car considered to have less than 160HP.