...check it out...
Might want to troll through a few dozen threads on building an M2HB .50 BMG. As stated,an M2HB is not really hard to do...if you have the right tools,time,experience and patience to do so. Also....it's a bit more $$$$ than other builds because of the parts involved. If you want to buy a 'kit',be prepared to spend about $6K,get the RSP,trigger/sear from KMP (TomT)...another $650-$700,and a rivet set. All-in-all,I have never seen a 'complete' kit...they are always missing a few parts/pieces...frustrating at best. Have built about 19-M2HB's and only screwed-up 1-gun...off-set receiver box. You might start by getting all parts for the receiver box first,as everything else will show up with a bit more frequency.
Best way...cheapest,anyway...is to aquire your parts over time,as they present themselves on ebay,gunbroker and gun shows. Usually it takes about 5-6 months to get everything to start an M2HB build doing it this way. I've built one for $2850.00 and most are about $3.8 along with the RSP and stuff needed. Good luck....and don't forget to ask questions along the way. Might also troll the m2hb.org site for assistance,as those guy's will help you too.