You're a bit far from Leeds, never mind 
Our tracks have been in areas about 20 x 20 m (ish), maybe a bit less. Really hard to judge in my mind's eye.
The one a Stainburn is built completely from site won material. The one at Thackley used about 100 tonnes of reclaimed top/sub soil and maybe 12 tonnes of single size 60 or 80mm dia limestone as the drainage media (plus some terram wrap). We also laid out the one STW did for their weekender feature a while back. No one was free to help dig though unfortunately and I think it's all been trashed by the Moto's.
Drainage is where it's worth putting some effort (which possibly means spending money as well) IMO. Digging a deep enough trench by hand can be knackering, a mini digger will do it in the blink of an eye. Similarly some mechanised barrow or dumper can make shifting the drainage media (or soil) a much less back breaking experience. We paid about £250 to hire a mini-digger, driver, 1 tonne self loading skip dumper and fuel for a day. You could probably get more for less but our guy knew what we wanted doing so was considered money well spent.
The easier you make the donkey work aspect of the build the more energy you'll have for the technical bit (getting berms to link, rollers properly spaced etc. IMO that gives you a much better chance of getting a good track, pretty much right, pretty quickly.
Hey Ho. All depends what you've gor on site / nearby, how much cash, how many bodies and what time.
Good luck and feel free to email if you want any other advice (timsellors[at]googlemail[dot]com).
