There are several things that we can safely assume with a transaction like this. First off it is going to involve a heck of a lot of money. Secondly both parties should be taking some risk - it really isn't fair any other way. And lastly buyer must be fairly serious or he wouldn't be willing to send you $5k up front.
If you want to sell these games and are not willing to take some risk it is very unlikely you will ever find a buyer. It sounds like you have a lot of time invested in this already so I really think in the end it just boils down to finding a number that works for both of you and then finalizing the deal.
One last point I didn't add to my previous common about this is you want to make it 100% clear the price is the price once you arrive with the games and you are not going to take a penny less regardless. Keep the deal & the delivery as two separate transactions (as if you already had the money for the machines and you are just acting as the delivery service - not the seller). So let the buyer know there will be NO wiggle room as far as your bottom line price right up front.
As far as the "right number" in my eyes that would be the cost of the rental truck, cost of motels & fuel, plus value of your time at "X" dollars per hour. Assuming you are driving the truck both ways the truck cost is likely going to be around $2500, fuel cost should be around another $1000, motels maybe $500 and if you value your time at a couple hundred a day add another $1000 for your time. So that adds up to around $5000. So looking at it from that direction I would say him sending you $5000 up front is fair to both of you. But again you are the only one who can really decide if it is worth it to you or not.
One last suggestion - instead of driving home with a huge pile of cash I would deposit that cash in a bank in his area and then once you get home move the money from that bank to your bank. If you belong to a bank that is a national chain that will be easy - if not open an account in a bank that has branches near him and near you. There is very little risk carrying a lot of cash if no one knows you have it but seller and GOD knows who else will know you have that cash (since you do know who all the buyer told about the transaction) so it isn't a good idea to travel all the way home with that pile of cash. We did shows for years and we know if several people who were robbed on their way home from shows because they were followed from the shows. In two different cases the vendors were killed over a day later while on their way home. To minimize your risk deposit that money somewhere local to him and withdraw it once you get home.