Israel doesn't operate the Egypt side and Egypt wants to not be an active participant beyond maintaining the crossing. They especially don't want to run a PoW camp.
Working with the IDF directly to transfer prisoners to them would probably start shit in Egypt Sisi doesn't want to start as it would be seen as entering the war I guess. Iran backed Houthi rebels in Yemen are already doing War Crimes on Egyptian hospitals for their current stance.
ID interceptor missiles are more like $50k-150k a piece, but multiple are fired during each interception to increase chances of a successful hit. The amount fired already since the 7th is still probably in the $1-2 billion range if you estimate conservatively.
Iron Knife and Iron Beam are much cheaper per shot (~$4 and $2500 respectively) but are developed by Israel itself in collaboration with US military industrial contractors. The Gaza war is a giant live fire test for them and countries including the US and India are lining up to buy them.
Iron Dome as a whole thing array also includes David's Sling and the Arrows which cover different type of attacks. I. E. Cruise and ballistic missiles amongst other things.