The Gazette reviews interactive tools in almost every issue. A site is generally made interactive using a programming language . Programming is much more involved than HTML and requires much more training. There are five general approaches you can use for adding interactivity. The hardest is also the cheapest, and vice versa.
Prices can range dramatically depending on the scale and complexity of the desired project.
This can take many, many hours, and can be extremely tedious. Furthermore, if you do not already know how to program, you will have to learn. For internet programming, I suggest that you master Perl and some JavaScript. Write the form that it will use. Find a customizable Perl script that suits your program's needs from one of the many free archives.