Forms of the metal bed has been used for centuries. It was regarded as the bed for royalty and the very rich bed in ancient times and was made of gold. The Industrial Revolution turned the metal bed into the bed for all people. The bed remains a favourite today and is available for those who wish to buy them. Saving money on a metal bedstead is possible, though it's a bit more challenging.
How far will you go?
One of the things that you must consider before looking for cheap metal beds, whether they're brass bedsteads or iron bedsteads, is what condition will you be able to accept them. If you are not handy or know someone who would be able to restore a bed for you, then you will have to limit yourself to beds that are in good condition structurally. If it's a matter of a loose or missing screws, that might be acceptable, but bent members or more serious damage would not. If the damage or condition is a matter of applying more paint or stripping the metal and starting over, that might be possible for you to consider.
Yard sales and rummage sales
Going to lawn sales or rummage sales would be good places to look, This is because you would probably be able to find metal bedsteads here more cheaply than at antique stores. The condition of the bedsteads would vary greatly, so inspecting them carefully would be imperative, keeping in mind your limitations as described above. Don't let yourself get taken by cheap prices for a structurally damaged bed that you can't repair yourself. You don't want to find that you need to pay the doubled price to get it repaired.
Classified and auctions
Classifieds are similar to lawn sales and rummage sales in that you might be able to find a good deal on metal bedsteads. The downside would be that you would not be able be to look at them in person. Ask to look at the bed beforehand. If the answer is no, then choosing another shop would probably be wise. Auctions might be a good place to look for cheap metal beds. You might also be able to look at the beds beforehand as well. The downside is that other people might be interested in getting a cheap metal bedstead which might raise the price beyond your comfort zone.