I would have thought you would, that does not seem excessive to me.
Whether or not you will be GLAD you have a field sharer is another matter... It's like flat sharing, but somehow worse I found. On balance, I would rather do without the additional money coming in and have the place to myself. It is better all round (for DH and the kids) than the seething resentment that always seems to build up after a period of time when others dont do their fair share of the chores...
Have reduced how many ponies we have but love the field which is now far too big. When full it costs £70 per pony per month for: sufficient acreage that you only need to supplement with hay for two months a year, a flat well drained riding area that is usable in all but snow/deep frost, two emergency stables, tack and feed room, mud free fields but no hard standing. Reasonable hacking.
So will i find anyone at that price? It was worth it to us as so close to home but is it too steep for what it is in the south east?