What are the most enjoyable games you've spent the least amount of money on?

I got Toree 3D and Toree 2 for 50 cents each on sale and had a ton of fun with them which got me thinking about how much I got out of cheap and/or steeply discounted games like Vampire Survivors, Paratopic, SNKRX, and some others.

So basically just the title, what are some games you spent very little on but had a great experience with?