Important Car Parts

My husband is a self proclaim handyman. He can fix almost everything in our house from plumbing, electronic installations to fixing a car. The reasons why we save a lot of money; instead of hiring someone to fix them for us, he does it himself. Am I lucky wife or what? Last week, he replaced the break pad of our van, changed oil and replaced the damaged window cause by the hailstorm. Now, he is planning on buying a bosch o2 sensor fr his car to help measure the distribution of fuel and air ratio in it. I wonder how much it will cost us to get this part for both cars. I guess, we just need to check it online or go directly to the places where they sell it. I just hope it wouldn't as expensive as I thought it would be for we don't have enough savings for it yet.