I had the K-20D as my first DSLR and I learned a real lot from it. It did not have the noise-handling strength of the K-5 and later models, but it did very well in normal light circumstances and with flash where needed. It was once the Pentax APS-C DSLR flagship model and it gave me some valuable learning experience along with excellent images. The body is sturdy and well styled also. It is definitely a learning user type camera that is sophisticated enough, plus shows nice performance.
Below is a shortcut to a used K-20D on Amazon in case you are interested.
https://www.amazon.com/gp/offer-listing/B0012Q94AI/ref=dp_olp_used?ie=UTF8&condition=used
Below is a shortcut to a K-20D/18-55 AL II lens offer also.
https://www.amazon.com/gp/offer-listing/B0015GEJZ0/ref=olp_twister_child?ie=UTF8&mv_style_name=1