PHP is the way to go. I found getting into it extremely easy with my previous good knowledge of VB and there are a lot of good websites (including the home page php.net).
PHP itself normally goes hand in hand with
Apache (web server) and
MySQL (database). All of which are free of charge.
The hardest thing really is security awareness and debugging because some of the compiler messages can be a bit misleading and you'll have to get used to the syntax rules.
Edit:
Incidently if you are looking for a cheap UK webhost to try out your PHP on, I use
www.idhosting.co.uk on thier £2.50 a month plan, I highly recommend them
Matthew Hall
www.indarkness.co.uk