I suspect the Nov and the Cyma that you mention will be good options (I don't know enough about the E&C to say either way), but plenty of other very good options for that price bracket, and many good options for actually a little less money. Some of the higher end Specnas, Double Eagles for example. Delta Armories seem to be churning stuff out at the moment too that I suspect is half decent (the fit and finish of the £35 Delta Armories receiver that I bought is really superb). The AR15/M4 style you seem to be leaning towards is a good option to start off with - a huge range of available guns, and one of the easiest to strip down and work on if you ever feel the inclination. Don't forget the AK platform though if you like the form factor - some very good options in your price bracket from the likes of Cyma and E&L for example.