+1 for a house party.
Most places you ring up about an 18th will just flat out say no, so your options are to pretend to the venue it's not an 18th, and risk half of his mates not getting in, rent somewhere like a GAA club and have the party end disappointingly early, or have a house party.
Get a marquee if you want, or just clear out your biggest room a bit, sort out some proper speakers, ask your son if any of his mates fancy trying their hand at DJing (about a hundred will want to), and buy a few frozen pizzas. You don't even need to buy drink, it wouldn't be expected of you, although a case of Lidl low percentage bottles wouldn't go astray. It's a much safer way of having the 17 year olds drink then borrowing their sibling's passport and having free reign at a bar all night.