Billy used a 77/78 IC big muff. So get one of them (they are cheap vintage muffs) off the bay if you like that sound.
otherwise the big muff with tone wicker is absolutely sick. An amazing pedal, its upgrades are simple as hell but its just excellent.
The current NYC is the 2008 model, it differs from the NYC most people have (if you've had it a couple of years as thats a 2000 RI) and it sick too, sounds different too.
if you like Pumpkins get an IC muff, you can get them for around $100-$150 on ebay if your patient and don't overpay! I got mine for $100.
Another thing to note is, if you over pay all you are doing is driving the prices up and people will start price gouging,l ike has been observed on vintage big muffs, jazzmasters and jaguars and is now happening on mustangs.
In the late 80's early 90's you could get 60's jags and JM for $500! now they are thousands!
I just got my second green (4th Sovtek) 1994 Sovtek muff (I'll be modding it as I hate the sound of them but love the look of them)in a trade (not for the WM I have in the ads section, but for another pedal I have). it makes 9 big muffs (plus two I have in pieces), a mix off modern and vintage and the one ramshead I made myself. Yep, I love Muff!