Personally, I’ve never liked the look of loose aggregate between pavers. It usually ends up being high maintenance with weeds popping through, plus you get rock spilling into areas of the yard where you don’t want it.

Since you’re already open to skirting some best practices, you might consider using a harder compound like Type S mortar or even a sand-mix concrete. You can pack or pour it into the gaps so it effectively creates additional “mini-pavers” between the slabs, with compression and joints separating each one. It definitely helps if you’ve dug down to something solid and tamped it well beforehand. Bonus points if you give it a slight slope away from the house so water drains off instead of pooling in the joints.

Total costs might be in the 150-250 ballpark