What are some cheap alternatives to amalgam fillings?

None. In most offices, amalgam fillings are the lowest cost permanent filling.
None Available. Amalgam is already the lowest priced material to repair a dental cavity. It's quick and simple to use, & less technique-sensitive, so it usually costs less than composite, ceramic, or gold. If done well on a tooth for which it is indicated, an amalgam restoration can last for decades...Well worth the money. Removing the tooth might cost less now, but replacing it later will cost much more.