don't be afraid to use cheap guitar, it's not a matter of price but more a matter of woods, pickups and overall crafting. If your guitar does sound great thru classic tube amps, you'll find some great rigs on the KPA too.
I use a 200€ second hand classic vibe Squier thinline tele (stock PUs) and it sounds really great with most of the rigs.
Remember that the KPA is 'transparent ' to your guitar and will emphasize it's flaws as well as it's qualities, just like a good tube amp does.
That said , the KPA deserves great guitars , once you get your KPA borrow some friend's guitars and listen to their actual tone thru the KPA, you'll be amazed by the differences and probably begin a guitar collection ( like japanese vintage tokais,orville ...)