In my area, we have vets offices (one is Banfield) that have these deals where you pay $x per month, and it's like a membership. It covers the annual exams, and it also covers any office visits. When I had my previous dog going there, the monthly amount was almost like a sinking fund. If you added it all up, you were basically paying for your annual exam on a monthly basis, compared to paying once per year. But, you get the added benefit of having the sick visits covered. So, we had a few sick visits, and they were pretty cheap because the office visit was "free". Maybe there are vets in your area like this?
Also, have you price checked other vets? I took my cat in for a sick visit recently and it was only $60. $150 seems high.