Are you wanting to build one or make one? The difference being that building would be gathering parts and 'smithing them together. Making would be cutting steel from stock using a set of prints. The reason I ask is that while building would be easier, and cheaper if you dont have a lathe and a mill, making is a whole lot more fun as well as difficult.
The thing to do is to figure out first what your plan is, in other words plan first and spend less. M2 barrels used to be cheap but the prices are climbing as they are not as easy to get. They also are not as accurate as it is a machine gun barrel. Some can be cut down and rechamberd, some are more trouble as the barrel might have a liner (stellite) in the chamber that cant be cut but can be ground. Also, in my opinion the breech threads are short and the barrel has to be supported further up as in the M2. You might want to look into getting a barrel blank from a barrel manufacturer. If you havent already, join the
www.fcsa.org. The magazine is great and you will also get a suppliers guide to all the manufacturers of 50cal stuff. Also, there is a message board for the members with a lot of the top 'smiths and manufacturers there on a regular basis.
If you are building, there are a lot of action and stock manufacturers. They will also inform you of some of the particulars of smithing a 50. If you are going to make your own, there are plans available from Gun Metal Design, Hyperdelivery Systems, and there used to be plans available for the Maddi-Griffin but I dont know if they are around anymore. Once again, the FCSA suppliers guide will be a source of info.
Just a caution, building or making a 50 is a challenging project. It will take more time and money than you think, but it is worth it. I started out just like you guys, I wanted a 50 but I didnt have the $$$. I ended up designing my own, spending a whole lot more time and money than I planned and wound up starting a business out of it
www.ferret50.com. On a final note, be sure to budget a nice gift for the wife, since you will be spending a lot of time in the garage on your 50.
Good luck guys and have fun.
Dave