I would go for a decent S/H Oxford oil cooled welder, mount it on decent trolley with yard proof wheels and spend a few quid on some decent extension leads. Its about the only thing that will take a battering in all the muck and mayhem of yard life and you will probably get change out of £150.
Things have moved on. GYS do a couple of MMA machines within your price range with pulse function - useful for positional welding if you’re not a great stick welder, the Gysmi e163 and the Progys 183e. If you want a useful bit of kit with 180a at a budget price some places are selling the Esab Buddy Arc 180 for less than 300. For farm use there’s always a second hand Mosa generator/welder..