Tack sheep, work in a few different ways.
If I put them on tack on your land, and it's fenced, has water, and you do all of the checks daily. Then it's 50p per head per week, and that's for good grazing or roots. With that, it's also your obligation to feed hay etc if we get bad snow, and they can't feed on the grass.
If it's crappy grazing, or I have to do all of the checks, etc I wouldn't be wanting to much more than 25-35 pence per head, per week.
For eight acres, if it's good grass, I would probably put something like 15-25 sheep on it for six weeks, let it rest, return etc.
It's not huge money, unless you have a good bit of land, and a good number of sheep in.
You may be better off renting it to someone on a different basis, i.e if it was well fenced, had water, i'd probably pay you up to £70 an acre or so, for the year. If it was handy, i'd probably give you £700, and top it, harrow it etc. If it was a bit of a pain, i'd be looking to give you more like £550.
But i'll tell you this for free, you will get more money from horse folk. . . . . . . but they will ruin your land, which will cost you a lot to fix. Or you take less cash from a sheep man, and in turn, they will improve (if done correctly) the land no end.