The problem with that is that the head may not come off so could be a little tricky getting your module inside it, also you would need a diver, as the driver for the 5mW diode would not drive the 100mW red
Another point would be that you would need 4.5v to run the driver & diode so a Lion battery would be needed and a spacer to take up the 2nd AA space.
by the looks of it he was going to swap out the diode for a 100mw, If you want a cheap host, look on the BST section there are a few that sell cheap kits, I don't want to name name because that would be unfair, but you could pick up a host and heatsink for about $15 for the diode if you want cheapness get this New 150mW 650nm Burning Power Red Laser Diode | eBay
I'm running mine at 250mA and burns fine :eg: as for the driver just read around here and you'll find something to suit your needs
You can Buy one or build one. Since your on a budget You should build one.
If you get the Heatsink from me i will send you some free LM1117 IC's and the correct ohm resistor for the diode i linked for you to build and put together. There are also 2 capacitors that the DataSheet says to add however i have never used them on personal builds and never had an Issue.