Your post suggests you're looking for the cheapest jackets. Be aware that in order to get costs down, manufacturers leave off things which we should consider to be more than optional extras - for example, crutch straps and spray hoods. I recommend very strongly that you buy jackets that have straps and spray hoods (read Ouzo report if you need more convincing)
Unless you and your crew are wearing loads of additional kit, or clothing that may change the positioning of your overall buoyancy (inc drysuits which could hold air around your feet and legs and cause them to float higher than a natural position), there is probably little need to look at 275N jackets
Why do you want a harness? Hope you're not planning to clip yourself on to a RIB