The pentax $2000 challenge
Hmmmm... I think this is a good starter kit http://amzn.com/w/269RRRYFZ02H
- Tamron 17-50 f2.8
- Tamron 70-200 f2.8
You can also add this for ultrawide landscapes if you can push your budget a little over:
- Rokinon 14mm f2.8
New total: $2150
The 70-200 isn't really built for ultra portability, but the IQ is amazing. The 17-50 is also amazing for the price. Don't worry about the 20mm gap between lenses (just use your legs to move around ;-))
Each millimetre on the ultrawide prime makes a difference and no need for AF on ultrawide landscapes really, you should have more than enough time to manual focus
Maybe add the Pentax teleconverter in the future if you need more reach.
Hope this helps!