Can I just ask why you would rather pay £300 on an non-sky box rather than just pay the £300 for the sky box?
(yes, they're not cheap, yet, well, the Pace DS180XE is cheaper now, but it won't work with sky HD, the same as other non-sky HD boxes)
But when you think about it, there's very little UK HD stuff at the moment, so personally I'd reccomend waiting a year or two before shelling out the money, just like with sky+, the price should drop as the technology develops (and sky work out any bugs in the boxes!!!)...
Not sure where you can get a new unsubbed box from (ebay I suppose), but yes it's easy to set up as it's like a sky+ box with just two inputs from the dish (use a quad though, you never know when you might want to add another HD or sky+ box or two SD sky boxes, or even a real satellite box!!! )...
Sky HD, TM6800HD, Manhattan Plaza ST550 and TM1500 CI+. 1.0m dish and 36v motor, Panasonic DVD HDD recorder and Panasonic video/DVD recorder. Sony G800 HD TV stand/surround system + Sony KDL40W2000. Infinity USB, Elvis, CAS1, CAS2.
The signals are way to weak, even with a really big dish (7 meters) it would be a real shot in the dark and you next door neighbours would be a little bit annoyed for blocking all that sunshine that they use to have before you totally eclipsed them with your huge dish! Also, the angle of which the footprint is transmitted to earth makes it almost unreceivable in North America. Even if you did put up a 25m dish, you still would need a European receiver, as the North American channels that you receive have different polarities(circular Left; Circular Right). But still check with your neighbours before putting up that dish.....
You have two options and one oher to receive SKY HD :
1. There are SKY HD boxes around for £210, unsubsidised. As new with warranty. Have one myself and excellent. Obviously you would have to subscribe.
2. There are various HD boxes around with CI modules, around £110 but you would require a dragon CAM around £60.
These are two good options, I do however agree with the other member that it is best to wait i.e. channel 4 launches in december, others wil follow suit, box prices will fall and the software will get better!!