Grill cover can you get a grill cover off Amazon for about 1/4 of the price of the KJ:

https://www.amazon.com/Mini-Lustrous-Ceramic-Premium-Waterproof/dp/B07YB9M5M1/ref=sr_1_11?dchild=1&keywords=kamado+grill+cover&qid=1606057765&sr=8-11

Pizza stones and drip pans are much less expensive from the ceramic grill store:

www.ceramicgrillstore.com

Cast iron: well any cast iron works. I made a less expensive version of the soapstone, just not out of soapstone:

https://www.reddit.com/r/KamadoJoe/comments/jse6xh/poor_mans_soapstone_review/

I like the stone better than cast iron because keeping the seasoning on cast iron in good shape has always been difficult for me. Stone is easier to keep clean and maintain in my opinion.

Hope these help you on your quest.