Reddit reviews Prevue Pet Products Mesh Bird Seed Catcher 13" H, Large Size

You can get cage skirts pretty cheap from most pet stores in the bird section.

It's important to have more horizontal space than vertical because budgies are not vertical flyers.

Here's a cheap good sized one

You & Me Finch Rectangle Flight Cage https://www.amazon.com/dp/B074P4T56Z/ref=cm_sw_r_cp_apa_R2dMAb30W4HYT

Here's a cage skirt:

Prevue Pet Products Mesh Bird Seed Catcher 13" H, Large Size https://www.amazon.com/dp/B004LOEQDI/ref=cm_sw_r_cp_apa_U4dMAbVBR6247