totally do-able if you're willing to figure out a work around using the existing PAX hardware or other, non-IKEA hardware.
I have several sliding doors in my home. I get the hardware from
Johnson Hardware. I also turned the STORDAL doors into a room divider using the stock hardware.
PAX uses a variation of a wall mount application for the sliding doors (vs. overhead mount...once you look at the JH website you'll understand what this means if you don't already know).
If you want to go the route of using the stock hardware that comes with the IKEA doors, keep in mind that the PAX mounting brackets and track are unique to IKEA and made to attach and work specifically with the PAX carcasses, so that hardware won't work without a little messing around. But I'm certain it could be made to work.
OTOH, if you want to start from scratch, JH will have what you need but you'll need to make sure you can attach it to the doors without damaging them. (their hardware is sold based on weight of the door and attachment method) Easier done with the wood varieties than glass/aluminium.
The other thing to consider is that the back side of the PAX sliding doors are not intended to be seen. Depending on the style, there may be holes or other "unsightly" issues on the wrong side.
As far as inexpensive modern interior doors, good luck. I've never really found any. One thing I've done is to use a solid core, flat slab door...no panels or moulding or anything. They're readily available in many species of wood and probably masonite, too. Paint them the color of your choice. I paid ~$120 for an eight footer from HD, special order, about a week lead time. If you're going to hang them barn door style, make sure you get them undrilled and without hinge mortices.