FWIW, we paid £200 each to Malaga last October, booking well in advance. That was through Flightline, with Monarch, but I discovered later that it would have been cheaper to book with Monarch directly, so you could look there.
Oh - it only goes up to March! (I'm not sure booking this early will get you a cheap flight anyway.)
You could try Jet2com, they fly Leeds-Bradford to Palma but their schedule only goes up to October atm. Ditto easyjet (Liverpool-Palma). I tried both for Sept fares (similar sort of mid-season iyswim) and they were quite a bit less than £250 round trip but depends on day and time, and they won't have May dates available until much later in the year .