I really don't want to sound negative, or offend, and what I am about to say is purely my opinion. The e28 was a fantastic car in it's day, and is becoming an increasingly rare sight on our roads. However, there is very little demand for these cars today, and only a very neat car (no dents, cracked dash, etc...) with a very low mileage (read 150k and under) will achieve a reasonable price. From what you describe, I reckon 15k to 25k tops is possible. Only an M5 will go for serious money and, to a lesser extent, a super tidy M535i, if you can find one. It's sad but, I fear, true. The same applies to other old BMW's such as the e12 and e23. Hope I am wrong, wish you luck with the sale, and would love to see some photos.