Smaller sections of land are almost always more per acre than the local agricultural land rate. Especially if suitable for horses :/. And of course, any land adjacent to one’s own holding has a specific value to you, which the seller knows.
Ragwort would make it unsuitable to most horsey people, but some seem to not mind it. There are expensive and rare Tennessee Walking Horses kept on land adjacent to my folks; the land is covered in ragwort and they don’t seem to worry about it at all. I think it’s more of a problem in hay, when the animals can’t detect and avoid it so easily.
Mowing ragwort is just about the worst thing you can do, I believe. Likely to turn a naturally biennial plant into a perennial, according to the info I’ve read.
According to my calcs, £35k is approx 160% of the upper end of your price per acre locally. Probably not out of order, in my experience. If you can pay up quickly, sounds like you might get it for less? Try ‘em for £30k, if it’s worth that to you?