You can search for "sold" prices on ebay which will give you a better idea of what something might sell for - if there has been a somewhat recent auction. If in doubt I always think - start the auction at the amount you'd be happy to part with the model for - then no one is second guessing and worst case you'll get that or it won't sell. If doing a buy-it-now come up with a realistic nice price and accept offers if you'd consider a lower amount.