Lots of places online have recipes for authentic flan, aka spanish custard. That, a simple caramel sauce,maybe some nice citrus zest and a mint leaf would make a very, VERY impressive and cheap Cinco de mayo dulce por supuesto! (for sure!) Also, if you don’t find an easy recipe and you’re not one who likes to cook, Jello has a powdered flan mix (but personally, I don’t reccomend it because it doesn’t taste very authentic.)