My favorite trick is to buy imported Gillette cartridges from foreign countries. These cartridges have been discontinued in the U.S. market but remain my personal favorite brand. I get my cartridges for around $1/each. Not cheap, but half the price of contemporary cartridges, and with far less plastic waste than fully-disposable razors. (I’m willing to pay more to protect the environment.)
As someone who fully shaves his head almost daily, closeness, speed, and minimal risk of injury are the most important factors for me. I’ve tried all the alternatives - electric shavers, old-school double edged blades with handles, etc. and found them either to not provide a close enough shave, or to be too high-maintenance or slow (too many passes required) to be worth the cost savings. Electric is out because I shave in the shower and they don’t cut close enough anyway. (Also, electric shaver blades dull over time, too.)