I bought K-x, then K-50, to 'get-into' digital, and able to use AA batteries when travelling.
Although it HURT, I have sold off all my M-series lenses (never had any K- or A-), because I got good prices for them, and only have so-much storage for camera gear.
Kept my favourite F- & FA- series lenses, bought K-50, set camera to allow manual rotation of aperture ring, and use in Av mode.
Bonus: if older Full-Frame lenses were a little 'soft' around the edges, this is not noticeable on the smaller APS-C digital sensor
Bought a Sigma 8-16mm DC Lens, for those really wide angles that my 17mm Full-frame used to give on film
Still have full-frame F- & FA- series lenses (& Cosina & Sigma DG), covering from 19mm to 320mm.
All work fine on K-50, auto, 'Scene', or AV modes (pretty much all I use)
But, it did HURT to sell the old M-series lenses.
However, I now find, with advancing years, that I use Autofocus a lot more, so no regrets.