If you can find a #2 hammer for a couple of bucks at a flea market, that's going to do just fine for now. Remember: accuracy first, power second!
If you're watching Trenton Tye's YouTube channel, you've probably seen his recent videos about using chunks of junkyard steel as anvils. If not, definitely worth checking out; certainly better than cinder blocks (if only in terms of durability). One thing, though: here on IFI, when we say "ASO" or "Anvil-Shaped Object", we generally mean something that looks like an anvil, but doesn't work like one (for example, one of those cast iron monstrosities from Harbor Freight), but when Mr. Tye says "ASO", he means something that works like an anvil, but doesn't look like one. Here on IFI, we would usually call that an "improvised anvil" or a "block anvil".