Hi, I can offer you a 3-tier/3-levels of security webapp, based on the web2py python framework, apache+ssl, mysql isolated db.
But, to precise the price of the offer and hosting, I need to evaluate the size of your current Access app.
Please get in touch via chat so I can evaluate, and then fix the final price in conversation with you.
I'd like to show you some samples as well.
Of course, you'll keep ownership of the schema and the data, and if you want, you can host it in your own server/hosting provider (must support python).
Waiting for your contact, best regards,
Esteban