Nothing secret here. That's the whole point of this forum. But look before you leap, unless you got cash to burn, and in my humble opinion, these days, that's the best thing to do with the horrible stuff. Not literally, well not yet, but I'm sure you get my drift!
£65 (inc. courier delivery) for a 5.25 litre oak barrel, complete with dripping wooden tap, waxed interior, varnished exterior, stand and bung. You discover the downsides later.
As per the C J J Berry bible, filled new cask with boiling hot solution of washing soda, and drained murky brown liquid which turns out to be dissolved interior wax coating! Furthermore, the exterior is varnished, so cask can't breathe, except through leaky all wooden tap. They used to fit non leaking plastic spigots, but people objected because it wasn't wood. No real problem at this stage as I intend to fill it with ******, which is actually not relevant anyway. The pertinent issue is improving home made red wine by storing it in oak casks for months, omitting the cheap and easy addition of oak chips.