Gerald is correct. It can be confusing to out-of-staters when driving down the freeway watching signs for fuel centers. If the price says "PUC" or "with PUC", that's only for commercial customers. So look for a displayed price without the PUC permit associated with it.
Right now the diesel prices seem cheapest at Safeway or Fred Meyer fuel centers, at least around Portland. I would expect prices in their other locations to be comparatively less than independents also. The problem with Gas Buddy is it doesn't necessarily distinguish between price classifications, ie PUC or not. Fred Meyer Roseburg is west off exit 125, and I think their price may be non-PUC at $3.84, but call them first and ask. The Fred Meyer and Safeway in Medford look like good candidates too.
Joel