$155 for 2 tires a good price? No. That sounds like its even slightly higher than the typical crazy high price you might see at an LBS.

I think last time I ordered from amazon they were $47.99 each, free shipping. From England you can get them for $38'ish free shipping from probikekit or ribble, depending on if there's sales and coupon codes.

I buy plenty of things from the LBS, but I doubt GP4000s's will ever be one of those things.