I'd suggest you save some money via searching the internet for similar items for sale , from current , as well as past closed auction results .
If you're looking to sell , you can use the above prices for a guide .
Some lithos (signed ones) were going up for sale in the 1990's for as much as $1000 ..... the market got flooded by folks trying to sell what they had , and prices dropped down as low as about $100 .
If you've got some provenance (other than word-of-mouth kind) on yours it would help a bit , come selling time .
What your reasons are for needing/wanting a certain type of appraisal will also affect the 'value/worth' of your items .
That's my two cents worth .