Order documentation and sales receipt is good. Price list is nothing special, same with advertising. They still make printer ribbons so its fine to toss them in but they are most likely bone dry. When you say some memory you mean Dip IC chips? I assume if you have an early 5150 it has a black PSU and a 16KB-64KB board, and those are the 16Kbit chips to upgrade? If they are from IBM thats a nice item to include.
Price is really what someone is willing to pay. I have six 5150's and one is an early model. I got all of them for under $150.00, most folks on here are in the same park, however having lots of good photos and showing original included documentation and the unit powered on and working you can accept offers on it. Take those photos and post them in the marketplace. If you were looking for a set price, there is no such thing.. Just find someone who wants it but they are not uncommon by any means.