what is the least expensive way to get started?
Lard Soap ingredients are not only readily available, but it makes darn good soap as well. You can buy
lard (Manteca, Armour, etc) and
distilled water at the grocery store. Lye can indeed be purchased as "drain cleaner" at Lowe's, Home Depot, Ace Hardware, Target and Walmart. Just be sure you're buying
100% Sodium Hydroxide crystals (NaOH).
Spend some time getting comfortable with an online calculator.
SoapCalc is the most widely used one. Follow the directions written in
Red at the top of the first page. Enter recipes that interest you to see how it all comes together. Once you understand the basics, you will be able to manipulate it to create the soap of your dreams.
My first time: Dressed in full "hazmat" (safety) gear, standing out in my open garage, with fear and trepidation, I added my lye solution to my heated lard, stirred with a $10 stick blender from Target and VOILA! I made soap! I poured it into a quart size milk carton. Unmolded and cut the next day. Honestly? I heaved a sigh of relief and never looked back!
For me, the journey began with a book I found in the discount bin at Barnes & Noble.
For you, I suggest you begin by setting a solid foundation by downloading and reading:
Find answers to most of your questions about start-up here:
https://www.soapmakingforum.com/threads/beginners-learn-to-soap-online.64426/#post-657018
HAPPY SOAPING!