There's a big rule when mentioning a price: "First one to mention a price LOSES". He's the seller HE should come up with a price first. Even if it's in the stratosphere (shock price to see what sort of fish he has on the hook) you can better deal from that stand point. If you give a price and it's too LOW, the seller could be insulted and won't deal with you at all. If it's too high, then you are giving away money you could use later.
$50 is probably much too low, $200 for both would probably be about right. $250 for a bucket truck/cherry picker is usually close to the going rate. But if you said it this way: "$50, because it'll cost me $250 for the bucket truck, and my time is worth $50 and hour, so I'll have $500 (stretch this a bit) in it before we are done". Don't forget to go to the hardware store and buy a gallon can of roofing tar to fix the holes left on his roof. You should do this just because.
Those dishes probably already have orthomode feeds, so there's probably not much you'd have to do with them at your place.
Maybe you have a friend that would like the second one, and could split costs with you?