Welcome!
Depends on your budget. You can get a K-r pretty cheaply (second hand or even new, while supplies last) and the K-5 (higher tier) also isn't prohibitively expensive, since Pentax just came out with the K-30 (mid-tier, I would suggest this one for "beginners" or if you want to use lenses without AF, because it has focus peaking) and K-5ii (very little difference from K-5, only newer AF module). If you prefer mirrorless, there is the stylish K-01, which has a lot of discounts recently. It doesn't have an OVF, though.
If you want cheaper (and older), you might want to check out the K200d. There is a camera reviews section on this forum:
Pentax K-mount DSLRs - Pentax Pentax Digital Cameras - Pentax Camera Reviews and Specifications
This lists all Pentax K-mount DSLR cameras and I think they are ordered by time (newest at top). Since these are digital cameras, newer technology tends to be better. Good luck!