We hired a mini and I mean tiny digger, a Kubota, £57.00 for the day and it easily went in and couldn't believe how powerful it was digging right down to about 7 feet but small enough to swing around with each bucket full and dump it's load in the skip.
7 hours from start to finish and the hole was huge for a 5 foot long pit but we were lucky as it was all clay and no rocks.
I've already got bookings from two mates to use it