The problem I see with the Mars is that there are still a lot of new old stock pairs sitting around. They never sold well and Oakley ended up warehousing and dumping them to wholesalers. I know a guy that bought 25, and still has 12 of them, all NIB. Who knows how many are still out there.
The other problem is that they are only an item more serious collectors are interested in. Unlike, Juliet, XX, Romeo, Penny, Half X, and X Squared, not too many people are buying these to wear them around town. Rarity does not always equal value as people often think, you also have to have demand.
You also have to take into account relative condition. Since there are so many NIB pairs floating around out there, anything less than that will take a disproportionate hit in value.
To be honest $250 is a fair price in the current market, but I've also seen some listed around that price that ended with no bids, some have gone into the $300 range. If your concern is loosing money when you go to sell them, I would not go more than $200, and they would not be my first choice if you are looking for an x-metal that is going to gain a lot of value. I don't like to buy anything for more than I can guarantee I can sell it for, others don't mind paying fair market value .
