Yeah! Go for UNIX!
Offer FreeBSD packages, or a linux distro packages. Recommended linux distro would be Slackware or Debian, Debian is awesome when upgrading and installing new software. Their package system is genious. When you want to update something, eg. Apache, you can type :
APT-GET INSTALL <apachepackage>
It rocks.. And all the software you need is FREE. Apache, MySQL, PHP, qmail/sendmail (i would recommend qmail), etcetc.
Let me know how it works out.
NB: You will find working on a unix computer very difficult in the beginning, if you are used to working on a Windows system.. But don't give up, you will make it in the end!