Cost to hire a Marquee

Help ! We are organising a family party and have booked a marquee for 80 people seated. Between different family members and a bit of disorganisation we had not budgeted the full cost and now it turns out to be much more than we expected.

Does anyone know what such a thing should cost. I feel that we are being overcharged because we didn't bargain properly at the beginning and now the guy thinks we are desperate (he is right).

Some friends who intended to rent a marquee for a family party ended up buying it as there was very little difference in the price of renting or buying.
By the way it has been used a couple of times since they purchased it last year.

Thanks for the suggestion Black Sheep

Well the party was great. We will know batter next time