Preston's guide

What’s the going rate for copy of the preston’s guide and where’s the best place to purchase?

Search on Google. I’m sure buying it online will save you some money. IMHO

I could be wrong, but think it is in the $60 to $80 range.

AHIT shows they sell them for $89 according to google search.

Go Here

You may also want to read this thread…
http://www.nachi.org/forum/showthread.php?t=9563

I got mine on ebay for about $35.00