Form building on existing website

Hi there, I am a French tutor and have a website which contains a page with a form so that prospective clients can contact me directly.
The person who has been designing the whole website has used FrontPage Extentions for the form but this program is no longer supported by our host (Fasthosts), which means the form isn't working anymore.
The problem is that my designer (it is actually not his specialty) doesn't really know how to use any other form builder program.
I am looking for a cost-effective solution that wouldn't change the presentation of the page too much if possible.
Could you please let me know if this is something you could do and how much it would cost?
Many thanks!

Stéphanie