Any idiom do you know means like"we'll do this one time but the hard way"?
I can immediately think of the following
Don't spoil the ship for a ha'porth of tar. (Old saying. A ha'porth was a half-penny-worth - a small denomination of currency)
If a job's worth doing, it's worth doing well (As mentioned by @Weather Vane)
A stitch in time saves nine (Traditional saying)