If you don't have plenty of disposable income, wait for a Steam sale.
Considering that it's the #3 top seller over all and #1 top RPG seller, and Skyrim's still in the top 10 (all that last time I checked), I don't think there's a great chance of that anytime soon. Maybe as a 10% off deal if you buy both together. Otherwise, you'll be waiting quite some time methinks.
On others comments about "could have" and "should have" been in the original game... uh, no. BGS released the game, you purchased it, you used mods to make it what YOU wanted it to be. If you wanted a custom developed version of Skyrim just for you, I can guarantee you'd be looking at Dawnguard (after hearing the price for your personally developed version) and nodding and thinking, "You know, that's a real bargain". And yeah, you'll complain that "but the modders give it to us for free". Have you considered that the modders HAVE NO CHOICE? Do you really think they wouldn't make money off of it if they could? AND, don't you think that, if they could, they wouldn't? Why? Because 3P dev houses would step in with mods and packs of their own They'd be big enough to be co-developed with BGS to prevent bugs, BGS would have right of refusal to "features", etc.
No, sorry, "should have been" arguments don't hold water. 15 hours of gameplay isn't worth it? I can't imagine you could have done both sides without rushing through in that time-frame, but whatever, 15 hours of gameplay for $20? Do you go to the movies? What's a movie ticket cost you? Does that ticket entitle you to watch it twice, or three, or four times?
