By the time you want to make a cut that far into the board you can use a straight piece of timber or better still a rail clamped to the board. Something like a spirit level might work.
Before track saws that's how a lot of carpenters cut sheet goods on site.
ah, right. yeah i think people are capitalising on the lack of these in the UK right now. maybe a covid thing? i paid about 50 i think
i thought you meant people were selling the home-made wooden ones for £150!
there's a million guides on YT for the home-made ones, but the principle is that you're using the factory edge of a board as your fence.