OP are you after cheap as possible up front, or long term?
If you get Gatorskins or Marathon Pluses they are more expensive up front than a cheaper tyre, but with a much better compound so they will last a long time. You also should enjoy the tyre more, and the puncture resistant comes are less likely to get a cut or sidewall failure. My rear Gatorskins probably last 7- months of 300k-ish a week cycling on road, trails and glass strewn cycle paths. Front about twice as long. Pull them off when they start to puncture, by which time they look like a dart board.
They may be £25-ish up front, but if they last much longer money well spent IMO. You could always look on
eBay for part worns, there are usually a few nearly new from people who tried and didn't like.
They are a love/hate thing though.