[pizza234]

Leetcode is probably the best resource (I've tried a few) for programming problems. They're very representative of real-world interviews (medium difficulty will do).

I'm confused by your judgment of the price. The Leetcode premium price for a couple of months is peanuts for an SWE.

Additionally, you'll need to add systems design studies, if required. This will cost you extra money, to spend at leat on Grokking the systems design interview.

Finally, it's extremely important to do mock interviews (which will also cost you, unless you decide to use pramp, which, however, is lower quality); while the experience of being interviewed on programming problems is not really different from Leetcode, systems design, and especially behavioral interviews, can be significantly different (in a "hard" sense) from what one imagines.