Id go straight to stage 3, your t3 will be fine at that upto 320bhp. Most genuine 3 bars are about £150, I've never used a BHP 3 bar nor seen a reputable tuner test one, I've seen his eBay add picture show him test them but they don't have any vacuum hoses attached so how can they be tested in the pic it doesn't make sense.

Take it your engines good?