Excluding textbooks for classes, I bought this for ~$300 (several several years ago as a special treat)
Most of my collection is thrifted/bought from garage sales (for a quarter to a dollar usually) but I do have a handful of nicer ones.
Personally spent? Around $15? Definitely between 10-15.
Most expensive book I have? Probably around $40-50 brand new.
I don't see any reason to buy expensive sets.