Brand new anvils can be prohibitively expensive for the budget-conscious blacksmith. There are wonderful anvils available from the upstart Nimba and the tried and true Ridgid/Peddinghaus. If you have the capital for it, you can't go wrong with a Peddinghaus.
For the frugal blacksmith, there are plenty of options out there for makeshift anvils. You're looking for a material hard enough and heavy enough to take the blows sent through the steel your working. When you're hammering a piece of steel, you're actually working it from two sides at once. The anvil is shaping it at the same time as the hammer.
I mentioned in an earlier post that I came across a piece of railroad track that a friend was willing to part with for free. This was an excellent find. My piece is 18" long and about 6" tall. It doesn't have the ever-useful hardie or pritchel holes, but for a beginning blacksmith, it does the job.
Pieces of track can be purchased on eBay for very little money. Some sellers will cut it to length for you. from a longer piece of track. Railroad suppliers are another place to look. They might not have the length you want, though. To save on shipping costs, it's better to find a local supplier and go down in person. Nothing beats a real-time conversation with a person.
Another idea is to look up your local steel supplier and see if they offer I-beams. I was in Columbus picking up some stock at Kroot Corporation and noticed some sections of I-beam lying around the warehouse. The advantage of I-beam is that it has a wide, flat face that can be drilled out to create your hardie and pritchel holes. It's also good and heavy. To mount it, you could either drill out the base if you have the right tools for the job, bend nails over the base or, if it has holes, use a chain like I did for my Quick Mount Anvil.
Need some more ideas? Check out Makeshift Anvils Part 2: Hammerhead Anvil