Timber is expensive. If you want a paint finish look at James Hardie groove lining boards. Vj panels. https://www.jameshardie.com.au/productrange/hardiegroove-lining

Have you looked at plywood sheeting with a black shadow line, something like this but without the metal beams

https://www.workshop.bunnings.com.au/t5/Whole-of-House/Love-this-plywood-ceiling/td-p/11219

You could check out this company also.

Some good suggestions above. I’d add the manufactured deck decking boards. They’ll never look at goo as real cedar but you may be able to get a look you’re happy with. Have you had a builder quote using dressed cedar timber planks from a wood yard? You could then stain/seal them yourself. It still won’t be cheap but may get you a mid way compromise.

Hi Aleisha Polytec make an MDF wrapped spaced Batten system in woodgrain finishes that could work https://www.polytec.com.au/brochures/polytec-steccawood-prefinished-decorative-battens.pdf but you need to make sure they did not get wet. Perhaps increasing the depth of your Fascia Boards would help with minimizing blow-in moisture?

Another option, which is actually totally waterproof is a woodgrain finish aluminium batten system like https://www.decorativeimaging.com.au/building-products/decobatten/?gad_source=1&gclid=CjwKCAjw-JG5BhBZEiwAt7JR64VrXGqEWPhS5NR1fYgfrjigV7FV51LflRdrY0IEkh4dVq_kXKBLPhoCOJoQAvD_BwE that you could install yourself. Cedar is very expensive and added to this is the cost of prep & sealing. Not sure how these alternatives compare in cost.

The Greenhaus Ascot Bamboo could also be a cost effective option, though I have found Bamboo Planks to be highly prone to warping and bowing so worth bearing this in mind with fixings if considered to be a option.

Hope these help, Malcolm.

I would use marine plywood.

This is an alfresco that has used marine plywood, with the shadow effect that siriuskey has mentioned.

And another.