If you're ok with 13t, BMX city to a sealed prolite left/right hub for about £15-20 quid, then you can get a 13t l/h freewheel, you will have to hunt one down, but they are available. good, bombproof hub for not much money.
If you want 9t, £70 won't get much new, but will get decent second hand if you can wait for the right one.
MM