It's worth checking your pressure properly, I went through a speight of 4 or 5 in a week until it dawned on me, a bit more pressure and it stopped.Are they punctures from thorns /glass etc or are they pinch flats?
But to answer your question, rocket ron evolution can be had for £25 if you shop around but they are not the most puncture proof tyres around, it's worth being sure of the cause of tth punctures first.
You say the tyres feel very soft, is that because there's not enough air in them?
It maybe that your tyres are rubbish, but equally it may be down to down to a lack of pressure, although that seems unlikely as you'd be getting pinch flats rather than penetrative punctures.
Have you checked inside the tyre carcass for debris, stuck thorns etc?