I sold my D.E Simpsons a couple of years ago for $2200.  It was in VGC and NO wear on playfield.

The D.E Simpsons is OK, but I think only worth around the $2000 to $2500 mark.  Privately they come up for sale and generally around that price.

A rough guide for restoration costs - to pay a 'backyarder' to fully rebuild the machine properly and 'shop' the game out you would be looking roughly around the $450 to $600 mark for labour and parts.  If a playfield needs touching up, this is a difficult process and there is only a handful of people doing it in Australia.

It pays to shop around and see what ALL the commercial guys have and are offering price wise and compare those to what are on offer for private sale.  Definately have a look under the hood of the machines and ask lots of questions before you hand over the cash.