Wendell and Jack at Ocean Aquatics sell Nanochloropsis, it's a super thick stuff, I used to feed just a few drops to my 90 gallon daily. I found it pretty reasonably priced, especially when you consider it's thick like ketchup.
If you want to really save some money, get some phytoplankton, rotifers and some Guillards from Reef Crew, you can feed rotifers, and green water to your tank.
Doug
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