Hi Cuilgypsy, Nila gave a cogent answer to you earlier. I would reiterate a couple things others have posted.
Of course, there is the customary question of 'what is the intent defined within the contract and did you meet your intended obligation?' Both in your home sale contract and that of the pest control provider.
First, there is no way any one person can know or tell a business as to what or how much they are should charge. This means you will probably see the re-inspection fee charged to you by Co. A. I wouldn't expect them to waive any fee. Remember, they did not get to do the work they bid on and have no profit to donate to your cause, beyond the money from the initial inspection.
Second, I would have made it clear from the beginning that you were going to keep the option of using another vendor if their costs were not affordable for you at this time. That way they have a better opportunity to choose the path to gain your business.
Third, Warranty probably has no standing here since, you are selling and moving out.
If you are obligated to provide Sec1 clearance to your buyer per any addendum or agreement within a contract then I would say you have met that obligation. Which leads us back to my previous question.
Which leads me to ponder; this is the essential purpose of having a full time Real Estate professional represent you. These questions rarely occur in the end...because the pitfalls are addressed in the beginning. I am sure your agent will help you.