Generally around the same price, maybe just a few quid more, or in some cases cheaper, especially if there is some special pre-order discount or something.
Of course, when it comes to Limited Edition or Collector's Edition packages, retail wins, due to the physical stuff you get, whereas digital, you'll obviously be missing that, but they'll always have some other thing thrown in for good measure too e.g. another game for free if it's within the same series franchise or something.
I'll take Resident Evil 6 as a quick example. When the PC version was to be released on Steam back in March, it was £19.99, if you pre-ordered, you get all DLC season pass, free Resident Evil 5, all due to bonuses. Retail disc version (Which will still use Steam anyway), was slightly cheaper from what I remember, but no extra fluff.