From time to time someone asks me for advice about buying an anvil. My first question is, “What are you using for a hammer?” It seems to me like a hammer and anvil are a pair of things which separately aren’t of much use.
Let’s get first things first. I once heard Steve Martin say, “Do you want to know how you can make a million dollars and not pay any taxes? First, make a million dollars. Then, don't pay any taxes!” In this case it’s, “First, get a hammer.”
If it seems the person is serious about buying an anvil for forge work, I suggest that they decide the hammer weight they will use most of the time. That will probably be 2.5 pounds plus or minus a half pound or so. I was taught, and have confirmed from experience, that a good forging hammer/anvil ratio is 1:40. Up to a point, larger may be better if the person is going to do some sledge work and has the extra money. But, the anvil mass issue can often be addressed less expensively in a good massive base.
After the size, quantity, has been sketched in then quality is the next thing to consider. Personally, I’d pick a London pattern shape and want it to have a flat face which is solidly welded to the body and has a good steel ball rebound. There shouldn’t be any cracks or missing parts.
I’d look for an old Peter Wright, Hay-Budden or Trenton brand. I don’t worry too much about some dings in the face edges or the top of the horn if they can be dressed and serve as a working radius or be filled. I take notice of the ring, first, to verify the steel ball rebound test. It shouldn’t have a “cracked pot” sound suggesting the face is delaminated from the body. Secondly, is it annoyingly loud and begging for a sound dampening device? That is a problem I have had with some of the new cast steel anvils.
I’d be willing to pay $2/pound for an anvil that suited me. Generally, I see asking prices run between $1 and $3 per pound.
This site has further information on anvil brands, age, etc.
This site discusses the physics of the hammer/anvil relationship.
The conversation would go in a different direction if I found the person was only looking for a unique door stop.