djchocice

I've spent roughly that on my car so far and would highly recommend what I've done which is:

Good Service
Yokohama AD08R's
Ferodo DS2500 brake pads
Tegiwa/Berk high flow cat (I've got a 70mm one but Berk make a 63mm one if you intend to stick with the standard exhaust.)
Air intake, I run a K&N FIPK as do many others on here.
Suspension geometry, it will bring the best out of those sticky AD08R's.
Aftermarket exhaust. I'm running a HKS 75mm Single. Paired with the Tegiwa high flow cat it sounds bloody horny, like a Mk2 Escort Rally car. However, there are many exhausts out there, if you desire one, find one that suits your wants and needs.
Trackday's!!!! The S2000 will make you giggle and yell with joy like a teenage girl at a Justin Bieber concert, it's that good.

har-vey

Honestly 2k doesn't go that far with these cars and without buying the car its hard to say what to spend the money on. You could spend 2k on getting it back to a good standard, brakes, bushes, oil etc so wont have any money left to mod. If the car is in A1 condition and your purely spending the money on mods then i would personally get yourself a good suspension setup. Many different option available and at varied price but the general rule is you get what you pay for. Meister R tend to be the good cheap option and Ohlins tend to be the more advanced quality option. If any money if left over and the car doesn't have one, id get a oem front lip as its a huge improvement on the cars looks.