I have none. I think if you can save money for a while and come up with enough to buy a 100 pound plus farrier's anvil (an older one) or something that's got good bounce, you'll be ahead and if you get in a pinch, you'll be able to sell it and get your money back.
The cheapest clean straight anvil I could find years ago was a soderfors pattern 125 pound anvil. It was $325, and would be about $500 now. I'd love to have a 250 pound anvil like it but the going rate for such a thing around here is about a grand.
Keep your eyes open for a good flat older anvil and save your money for a while instead.
Not sure if you could find a large piece of hardened plate that you could attach to a base and use like an anvil, but would be surprised if someone made such a thing flat and it was much less than a decent 100 pound anvil.