Oof...you really wanna know? Probably upwards of $2k...definitely not under $1500 unless you're good at giving hand jobs.
Seriously though...these things are money pits lately. Judging from what Mac is saying it wasn't always this way. My next one I'll be barreling/timing/headspacing myself. I just bought all the tools I need for the job after finding out the ones I borrowed won't work for the M14 (thanks anyway though, Mac). And if any of you guys just want to take advantage of buying a standard receiver (not xm21), than you can borrow the tools from me to barrel it down the road.
The biggest costs are obviously the barrel, bolt, trigger group, op rod, gas system and depending on what you get for a stock, that could be up there as well. The small parts can be had for wicked deals on the M14 forum, you just gotta check often and be the first to jump when something goes up for sale.
There are a few nice wood stocks in the classifieds on NES right now for short money.
Truth be told, you're just not going to get the accuracy out of one of these that you would out of an AR platform...not without throwing a TON of money at it, anyway. If you wanna build one for the experience...because it's 'fun'...that's the reason to do it. I had WAY more fun building my M14 than I did any of my AR's...took about 8 hours all together, but I was moving right along I was so excited to have a finished product in front of me. Do it piece by piece and I bet you won't even notice how much money you're wasting...ahem...spending
ETA...the barrel vice I got is for medium contour barrels...keep that in mind if you're wanting to buy stuff now and borrow my tools down the road when you're ready to build.