+1 for building your own if you have limited space. I started with a z-axis column I found on craigslist and have pieced it together from that. Obviously if you can start with a working machine you'll be able to build many of the mechanical components you need for the conversion yourself. I'm assuming you're not planning on converting your PM727?
I can see the appeal of the kits that are out there but many of them just package $400 worth of stuff and sell it for a grand. Looking at the one you listed there's nothing special about the pieces in that kit and there's still an awful lot of stuff you'll need to do to hook it up to whatever machine you buy. I started out with a $20 controller card, parallel pci card for my old pc, three $10 drivers, some donated nema 23 stepper motors and old laptop power supplies I had laying around. I got my machine up and running with the original column I bought, a fabricated base, and an X-Y stage purchased off eBay. I use LinuxCNC to control it all and don't have experience with the other systems but have been happy with the flexibility and ease of use with it.
Since then I'm in the process of upgrading the Y axis and have decided to switch to a Mesa Electronics Ethernet controller for better documentation. I will probably also eventually upgrade my drivers and steppers too. But, I really wanted the learning experience of building this thing and I'm willing to spend my time improving it as needed. If I wanted to start producing parts right away I would definitely go the route above with buying an existing machine and upgrading the electronics.
As you'll find with any "what machine should I get" question on this forum you really need to figure out what you want to build before you start shopping. I'm assuming from your username that you're into paintball and probably wanting to make new gear for that hobby. What materials will you be working with and what is the maximum size part you anticipate building? It's pretty easy to overestimate the jobs that can be done on a small machine so understanding the limitations of what you are looking at is critical to avoiding disappointment.
I'm sure many of us understand the difficulties of an expanding hobby with limited shop space. I recently moved some of my mom's stuff into storage so I could have more room in the garage. Now is a good time to have the discussion with your spouse about how much space, time, and money the hobby machine thing will eventually consume. Most wives welcome hobbies that don't include spending time away from home, or fast cars, or other women
If you have ideas that can eventually become a source of income that will probably be appreciated too.
Good luck, and don't settle for half a solution.
Cheers,
John
