The problem using a skillet is it's shallow. If you use a ladle to transfer to your ingots, it will be time consuming compared to a dutch oven. But, yes, you can certainly use a cast iron skillet. You'll still get the job done.
How much lead to you have to process? I use a 2 quart Revereware saucepan and a 1000W hotplate to render scrap lead. It handles about 10 to 15 pounds at a time easily and is faster than it sounds.
You have a Harbor Freight in your area? Do you receive American Rifleman from the NRA? They have a coupon in there for HF. You can get a 5qt dutch oven for pretty cheap there with a coupon...
Using the Bayou Classic turkey fryer from Home Depot works perfectly. It has the same basic grate pattern as most other fryers. I position the feet between the grates and have no problems at all...
Find a thrift store. I bought a 24 quart stainless steel stock pot at one that cost me a whopping $3.25. I use it for melting down wheel weights to pour ingots. For casting I use a 6 inch cast iron skillet that is 3 inches deep. Price othat one was 50 cents at a garage sale.