Anvils come in all shapes and sizes. There are good quality ones and others that are good-enough-to-get-the-job-done. You can also use a piece of railway tie that has an incredibly hard surface. Some vicses have a flat surface that may be usable as an anvil. We started with a 100lb anvil from Princess Auto and still use it to this day. They are a good place to look for a starter anvil if you want to purchase something new. Yard sales and auctions are good bets for second-hand ones. Some people say don’t waste your money on a cheap anvil. I say any anvil is better than nothing! You won’t get much armour made without one.
You can test the quality of an anvil by holding a hammer and letting it drop on the surface by its own weight. The hammer should bounce back 2/3 the drop distance. it should also have a bright ringing sound rather than a dull thud. Just because an anvil is old, doesn’t mean it is a good anvil.
The anvil is only as good as the stump you put it on. Be sure it is good and solid. Use chains or steel brackets to attach the anvil to the stump! Using an anvil on a tabletop just doesn’t work!