Is paying $3500 for 1998 Audi A4 1.8T Quattro to much?

well if i were you have them take it to the audi dealership and inspected. Second i would do is do your own visual walk over such as broken bolts in alignment slots odd noises like loud ticking under the hood excetra. for a low miles audi 3500 is a bargain and the ac you can fix that quick and easy as its most commonly just needs a recharge. but check the condenser for oil like spots in the front rad as mine had a pin size hole and its easy to spot once you open the hood. But for a professional opinion on the car just take it to audi and ask for a full inspection or saftey and that should tell you what your getting into. i know my 98 a4 v6 2.8 quattro needed mnor work at first but its hitting me hard now due to high miles i recently broke 360k on mine and she is still running strong. Oh and major major look into ask about the timing belt and get that inspected if it every looses that then you got a 3500 $ paper weight. 120k is ussaly the time for a timing belt change and that can be costly was 1400$ for my v6 the 4 banger is a bit cheaper. Timing belt is the number one check on the car. hope that helps

oh and if its been parked for a long time have the brakes checked the calipers have a habit of sticking over long sitting periods