There are a few members who have went for power through the NA route.
All of them have given up after spending a small fortune and not getting anywhere near the gains they expected.
You say you want to keep the budget to a bare minimum......a minimum for what? What power/torque figures do you want to achieve?
£6k is nowhere near enough to get 380 at the hubs. Christ, if that was the case people wouldn't spend £7-8k on superchargers.
I'm sure someone here has a built NA engine and managed 340hp at the fly after spending a small fortune actually. Think it may have been for sale.