Originally posted by Timd Nikon has some cheap lenses, but they are so-so. The excellent Nikon lenses make some Pentax lenses look cheap. With Pentax and Nikon, you get what you pay for.
I'd contend that Nikon's cheap primes are excellent and an awesome value for their performance.
From B&H's current prices:
Nikon 35mm f/1.8g $196.95
Nikon 50mm f/1.8g $216.95
Nikon 85mm f/1.8g $496.95
Pentax 35mm f/2.4 $216.95
Pentax 50mm f/1.8 $246.95
Pentax 77mm f/1.8 $1,046.95 (no 85mm currently manufactured, so this was the closest lens).
The prices don't seem that much different, but when you factor in that Nikon gives you a 5 year warranty versus 1 year with Pentax, it makes you wonder why Pentax isn't cheaper. And then you really wonder when you consider the Nikons above all have SWM for silent focusing versus the old fashioned screw drive of the Pentax lenses. Even DXO confirmed that these cheapo lenses (save the 35mm because it's crop specific) all performed as well as their costlier cousins when they tested them on a D800
here.
As for zooms, you do get what you pay for, but you don't have to pay full price. You can often get a $300 to $400 instant rebate on the fast zooms (14-24, 24-70, 70-200) when you buy them with a new body during the holidays. And if not that, the used market is plentiful.