Savings tips - trying to save 50k in a year for extension

Hi I have a savings goal with my wife to save for a large 110sqm extension an house refurb in southeast.

We are early 30s if it matters.

We have combined 305kish in our isas in MMFs. I think they earn about 3.5% interest net of everything so about 10k/y.

5kish in cash

The extension will cost about 350k with contingency so we are trying to save about 40k from now til the end of the build, about 3-4k a month.

I think salaries net about 100k after deductions plus the 10k from interest.

We are paying 1.5kish to live in our flat, and 3kish for the house (currently vacant and cant fill it currently).

We are living very minimal lives which we are fine with, and aiming to spend next to nothing other than on food and travel to work.

Does anyone have any good savings tips/tricks to get significant savings?

We currently use tesco clubcard plus which is £16 and gets us about £32 off our monthly shop.

We also shop specifically for clubcard savings. We cant shop at lidl/aldi as we both eat only organic meat for ethical reasons.

We have a cheap car and dont drive much.

Any tips appreciated.