3000k are more on the red end of the spectrum and are idea for flowering.

6500k are more towards the blue end of the spectrum and are more ideal for foliage plants.

not sure why they're more expensive. Maybe because they usually sell those as "bright white" and they could be more popular for normal non growing.

3000K (anything in the 2700K-3000K range) is usually described as "warm white" and has a yellower look to it, more like old-timey incandescent bulbs.

6500K is usually described as "daylight" and has a bluer look to it.

In between is 4000K or 4100K "cool white." These are bluer than the "warm white" but not as blue as the "daylight". "Cool white" is the traditional fluorescent color that has been around for decades.

For grow light applications, there's marginally more blue in the 6500K spectrum and marginally more red in the 3000K "warm white" spectrum. Almost all fluorescent tubes are "full spectrum" and contain a lot of visible light that isn't really needed/used by plants, and not so much of the specific colors/wavelengths that are absorbed by chlorophyll and used by plants. Specific wavelengths in the blue band promote green foliage growth, and specific wavelengths in the red band promote blooming.

If the technology, brand, wattage and size are the same, the color temperature should not affect price for fluorescent lamps/bulbs. Are there any other differences that might explain the price difference?

I think the amount of cool white and daylight tubes produced is a important factor