Kmount lenses that could be used on a Pentax K1000 can be used on any current or recent 35mm style DSLR. 
Totally manual lenses (without the "A" auto-aperture setting, my require adjusting the menu settings to "allow use of aperture ring". Because recent Pentax DSLR's do not have viewfinders that enhance manual focusing, the LCD panel and live view may provide better results than the eye piece in low light.  Because the K1000 used the 24x36mm (35mm) film format, any lens that did not substantially vignette on your K1000 will cover all the Pentax DSLR's APS-C sensors and those with "full frame" sensors as well.
What the old lenses are unlikely to have is weather/dust sealing and because current Pentax DSLR's come with weather/dust sealing standard (even the least expensive), it may be worth considering adding one of the weather resistant ("WR") kit lenses to your bag to broaden the range of conditions in which you can shoot. Several of the "WR" lenses are inexpensive new and used.
: the Pentax 645 medium format DSLR's are another matter and present substantial tradeoffs, but you probably won't be buying one of those if cost is a consideration.
: On the other hand, I've achieved acceptable results manually focusing in daylight using the eye-piece.