I am a Surveyor of several decades experience. I pretty much stick with military surplus trousers and such from places like Sportsmanguide.com for field clothing.

The work is very hard on clothing, and eventually everything gets snagged on a barbed wire fence, or sticker bushes, or worn from scrambling on rocks or down slopes, etc.

Which is to say that BIFL isn't happening here, at least not for trousers.

I do spend good...very good...money on boots, but with trousers I go cheap military surplus and consider that even those won't last forever.