www.cd-wow.com has the Angel ones for £27.99, and the Buffy ones for £30ish.
Only on region 1 though, and there's a chance you'll get stung for customs charges (i have the last 2 times i've ordered them, was £9ish for me each time..)
If you don't mind all Region 1 versions, without a doubt "Enterprises DVD" are cheapest for them all. I got stung on Customs Duty from CD Wow on first Buffy Season. Since then I have used Enterprises with no problems and no Customs Duty or Shipping charges. All Buffy boxsets are £35-£40 or less and Angel boxsets priced much the same.