Mate, I'd say those prices are to be expected on ticket broker sites. You'll not get a ticket as a non member for anything remotely cheap that way.
Honestly, your best bet is to get yourself to Wembley and get asking around the pubs. There are always people in large groups of pals who fail to show, or get so pissed up they are incapable of getting in.
United usually get allocated The Torch pub. Get yourself there and ask around for spares from about three hours or so before kick off.
An hour before head around the ground, a 10 minute walk. Wander around the united end of the ground, and see if anyone has any spares.
I did this numerous times before I was a ST holder. I'd say 7/10 games I'd end up with a ticket. The only times I didn't were for Champions League final and a League Cup final and a handful of aways. Otherwise I was sorted, usually for face value.
Otherwise it's touts. You'll pay less to a tout on the day...but you have to be careful about snide tickets. Usually you'll be fine...no touts would want to get name for selling fake tickets, but obviously if you get to the turnstile and it's a fake or a cancelled ticket...you've lost your money.
Good luck pal. Hope it works out.
We're the other end this time mate, so that will be a Spurs pub.
Our main pub will be The Green Man. Speaking of which, I wonder how early we'll have to get there before it's already jam-packed. Atmosphere there was incredible for the semi vs Everton couple of years ago
Allocated Pubs
Man Utd
The Green Man
Dagmar Avenue, Wembley, HA9 8DF
Blue Room
53 Wembley Hill Road, Wembley, HA9 8BE
The Arch (Greyhound)
324 Harrow Road, Wembley, Middx, HA9 8LL
Station 31
299-301 Harrow Road, Wembley
JJ Moons
397 High Road, Wembley, HA9 7DT
Thirsty Eddie's
412 High Road, Wembley
Flannery's
610 High Road, Wembley
Fusilier
652 Harrow Road, Wembley, HA0 2HA
Masti
576-582 High Road, Wembley, HA0 2AA
The Comer House (Mannions)
313 Harrow Road, Wembley HA9 6BA
The Liquor Station (Old Bear)
397a High Road, Wembley, HA9 7AA
Moore Spice
Unit 2, Wembley Retail Park, Engineers Way, Wembley HA9 0EG