How to spend $300 - $500 to upgrade my Breville Barista Pro Set-Up?

I've been getting pretty into coffee this year; I really love weird co-fermented/funky espressos. I'm trying to upgrade my coffee equipment, but not ready yet to purchase a new espresso machine.

What can I do to upgrade my current set-up? Any modifications to the Breville Barista Pro/grinder?

I usually drink co-fermented light roast beans and make them into an iced latte. I've been starting to host coffee tastings around this, so want to really up my espresso game to be able to pull off the best coffee I can. I have a budget of around $300-$500, thinking I could spend it on a grinder and maybe a few modifications to the breville barista pro.