PROGRAMMER TO FIX OS COMMERCE PHP WEBSITE

We are a small business with a custom designed OS Commerce PHP website. We have an SSL on our website, but pages with products on them show as "not fully secure". We were told by our hosting company that to fix this we need a programmer to go into each product page, inspect the coding/links in each page, then change any pages with links that show as "http" to "https" to make them secure. Alternatively, a programmer may be able to do a “sweep” of our site and instantaneously change http to https in one action. We have approximately or less than 2175 pages of product on our website. Coding/links with “http” on product pages may be but also may not be what is causing the product pages on our site to show as “not fully secure”. We want the programmer we retain before moving forward with this project to enter the site at no charge, change the coding/links on one page from “http” to “https” to confirm doing so will lead to the page showing as “secure”, and that no other problems or errors will result from this change. If the programming change does fix the problem and lead to no other problems/errors, then we would move forward with the agreed to project at the agreed to price. If it does not, then we would not move forward with the project and we would have no obligation to move forward with nor pay for this project. If it does not lead to the page showing as “secure”, then the programmer has the option at no charge of diagnosing the problem, detailing what needs to be done to fix that problem, then providing us with their best estimate to fix that problem. We would then contact other parties at that point to verify the accuracy of the diagnosis, and to solicit quotes. We would give preference to the programmer who did the initial diagnosis, but we would have no obligation at that point to move forward with the initial programmer nor any party. We would prefer a flat budget but would be willing to consider an hourly rate, or a combination of a flat budget and hourly rate to get this done. A confidentiality agreement acceptable to us must be in place prior to us beginning this project. We would like to move forward with this urgently. Please provide us with your estimate as soon as possible.