Stove Conversion is only the Beginning
The real expense is in adding everything you need for LPG including a suitable locker, solenoid, alarm, etc.  Figure on about $400-$500 in parts.  An alarm isn't required and I've seen pretty new boats without them, but I wouldn't skip it.  It's about $200 in itself.  Seaward makes a nice locker/tank/solenoid unit that I bought at West Marine for about $200 a few years ago (it fits in my C-30's stern lazerette).  Check out West Marine's website for their "Advisor" on LPG installations for some good info.In running my gas line, I bought some clear plastic water hose to run it through to protect it from damage.  I also thought of using plastic sprinkler pipe as a conduit where it ran through the port lazerette, but decided on the plastic hose since it would flex around corners and I could use it for the full run.