Check out KameSame. You can go through the exact same content as WaniKani if you want, albeit without the extra teaching information and userscript support. If you really need a more frugal substitute, then this is it. I almost decided to use KameSame without WaniKani myself, just to circumvent the hard speed limit, but ultimately I feel that the tools and information provided by WaniKani are more than worth it.
WaniKani only builds recognition, so even with a WaniKani subscription you should still use KameSame since you can import your WaniKani items as you learn them and practice recollection as well.
These scripts were the deal makers for me:
WaniKani Lesson Filter - reorder lessons by item type (critical for “speedrunning”)
WaniKani Ultimate Timeline - adds transparency to upcoming review schedule
Double-Check (Version 2.x) - correct typos & brainfarts
Stroke Order Diagram - Learn to draw the Kanji!
Jitai (字体): The font randomizer that fits - Don’t become illiterate in all but one font!
WaniKani Pitch Info - understand pronunciation a bit better