I love how "we" should be happy to over pay because "your" paid 4500 each for them.
I am in sales for a living so I am the first person to respect commanding a higher price for an item. That being said, it has to still fit into what the market is willing to pay. Best of luck to you though, I hope you get it!
Remember we're looking at a miner willing to part with his equipment while it's still profitable. Being in sales for a living, makes you have different targets than he has.
IMHO a sales guy tries to make a sale no matter what (get the best price for whatever he has to sell), while an operations guy tries to make a living from managing his equipment, avoiding downtime etc.
One SP30 at this point makes around 1 BTC per month .. you can expect about 25-30 BTC/mo (conservative) from the whole lot. Everyone does their own calculations.