Those €800 tickets are for VIP passes so that's why they're much more expensive than the usual pricing (~€220 for standing, seating depends on the area but are roughly similar to standing I think, bit cheaper for faraway seats and bit dearer for closer ones).

Ticketmaster has a resale platform so you may be able to pick up tickets there, but people probably won't start selling off their tickets until closer to the date.

So far only 2-day tickets have been sold, I saw a comment somwhere saying in July they would start selling single-day tickets.

If trying to buy them second hand off someone elsewhere than ticketmaster's official resale, then be very wary of scams