There used to be a big camping field just north of Benllech - not sure if it's still there but it was on top of the cliff overlooking the sea so stunning views. No facilities and £3 a night - but that was 20 years ago
Was on Anglesey last July and NOT many small sites, stayed on a ccc cl but can remember the name but its now gone private, had 3 parts to it when we were there 1 was private 1 was CC 1 was CCC, will see if I can find the name as we were £15 nigh with EHU
you could try TY Newydd just outside benllech has nice friendly staff, small bar and showers and loos are all ok, its not far from the rugby club and on a sat morning there is a carboot sale there! last time we stayed it was aprox 17 a night.