You may also want to visit your local FedEx or UPS store and ask about boxes and packing material (bubble wrap, foam, etc.). You may want to ask for an estimated ground shipping cost and choose a state that’s a pretty good distance from you. This should give a slightly high “average” cost.
If you post it on Ebay; make sure you tell the potential buyers that they will be responsible for the shipping costs in addition to the cost of the unit if you don’t want to have to “eat” the costs of shipping. This is a fairly common practice from individual sellers on Ebay.
I typically use whichever is the cheapest one (FedEx/UPS); round up any odd amount to the next $5 (11.00-14.00 = $15), and then add an additional $5 to make sure any unexpected costs will be covered.
Also; if you would prefer to not have to ship international (customs can be an issue); you should disclose any restrictions on the sale.
Example:
“This product ships FedEx ground to anywhere in the United States, except Alaska and Hawaii. International shipping is not available. Buyer will be responsible to pay an additional fee of $$.$$ for shipping and handling.”