Grammar 以为

以 (noun/adj) 为 (noun/adj) : To take (something) as (something)

开车的时候，应该以安全为主。
kāichē de shíhòu, yīnggāi yǐ ānquán wéi zhǔ.
When driving, you should consider safety to be most important.

This is a classical construction; don’t try to logic it out too much & accept that it’s not really flexible (no 为…以…). 以___为主 is particularly useful for talking about priorities

现在他找男朋友, 以幽默感为主。
xiànzài tā zhǎo nán péngyǒu, yǐ yōumò gǎn wéi zhǔ.
Right now he’s looking for a boyfriend, (for him) a sense of humor is most important.

Almost elegant really. Which brings us to the piece that is in the text:

…那就物以稀为贵!
nà jiù wù yǐ xī wéi guì!
well (people) take scarcity as valuable!

“物以稀为贵” is also an idiom but you see how it’s built now :) As a structure, this isn’t aggressively formal, but it is more written than spoken. Happy Thursday hope you’re well!