Splid is great. Simple yet feature-rich if you need it. If you want to create many different groups for splitting it’s just a small one time fee instead of monthly. If two groups is fine or you just want to join groups it’s free.
And best of all: there is no need for an account! In fact there is no account you could create.
Update: Missed in which community I’m in. The App sadly isn’t FOSS and isn’t in the fdroid-store. But it doesn’t change my opinion about it :)
I know it only as a german expression for something extremely common or regular. Apparently it was a type of machine gun used in WW1 and WW2 that was the default weapon and / or of lower quality.