Hi Lynn and welcome to the forum!
A Pyrex measuring cup is commonly used for lye mixing. These tempered glasses are safe up to boiling temperatures. I use a 2 qt. measuring cup dual use food and soapmaking, washing it twice before returning it to food use.
Steel pots are the ideal container to heat your fats and mix in the lye. An enameled iron container is the least expensive choice. It would probably be better to not use this container for food too, but I suppose a careful and thorough person could. I got a 2-1/2 qt. steel double boiler pot at Bed Bath & Beyond for about $12 after applying a coupon.
Neither aluminum nor iron should be used for soapmaking because lye reacts with these two metals. Utensils and containers should be steel, glass or corrosion resistant plastic. Wooden utensils may be use but the lye eventually ruins them and they have to be replaced.
A family member gave me an unwanted 8 qt. stock pot and I have my own 12 qt. stock pot if I want to go the wash really thoroughly before returning to food use. Steel is practically indestructible so you can get very radical about your cleaning methods.
I got a large crock pot on sale at Sears for $20. A Euro-Pro model, made in China. Go figger.
I found that it was easy to get all the basic gear cheaply if you're willing to shop around. Sears, Walmart, BB&B if you have their 20% coupons, and don't forget to check out restaurant supply stores. There's no reason why anybody can't get all the equipment they need for about $100. Maybe a bit more if you have to purchase a large steel pot brand new (about $50-$80 depending on size). The inexpensive enameled iron stock pots sold at Walmart are the least expensive mixing containers.