I have Ultegra R8000 groupset on my road bike. When shopping for cassette for direct drive trainer, could I got with 105 R7000 cassette to save some money? Are there any differences, other than weight?
Absolutely, any Shimano or SRAM 11 Spd cassette will work.
No problem at all with 105.
They will be functionally identical. The only reason I have an Ultegra cassette on mine is that I wanted to replace it for another with more suitable gearing anyway. I would also consider using a narrower cassette, such as an 11-25. That allows you to more easily adjust your cadence if need be.
Just my anecdotal experience over the years - 105 cassettes don’t last as long as Ultegra cassettes. Dura-Ace, although lighter and more expensive, also wears quicker than Ultegra. The Ultegra cassettes seem to get good heat treatment, are built for durability, and are a reasonable price. So Ultegra is my sweetspot cassette. Whatever my bikes, when I need to change the cassette, I get an Ultegra one.