If you haven't got a turbo timer ...>> get a blitz Dual DC II. It has a digital boost gauge built in. I removed my aftermarket boost gauge after fitting my my turbo timer. Only problem is it displays kg/cm2 but once you get used to that it's fantastic.
How much do you call reasonable? there are Matrix Colour Switchable Boost Gauges for about $60 from AutoPro... Then There are Autometer Boost Gauges from about $110+ on TTZ Both of these are in PSI not Bar if you are looking for Bar readings then all Jap brands eg HKS, Blitz etc put those types out, price for those types are from about $150-$200+
