Hello! If I understood you right, you want your MS Access and VBA program to be re-done via some web programming language, like Java or PHP perhaps, or maybe Python, potentially using some frameworks or CMS. You also require that the new software is capable of being used as SaaS, which means you will probably take some web server and host subdomains to whatever your site is for each client, or issue usernames for individual clients that will allow creation of other client logins.
I can do all of that with ease, however I think much time will be spent on testing all functionality after the beta version, which you requested in 3 weeks. That's why I am putting the same amount of time on testing. 21 days until beta + 21 days until final version. Unless your specifications are very detailed and clear there will be much to decide on the go, and I can provide you with required consultation.