Trapezoid Window - blind/curtain suggestion?

[kmini]

What are the window treatment options for a window like this? Imagine two large windows like this but the top is partially flat. They mirror one another. I know plantation shutters are an option, but I would like to find a more cost effective option. Any recommendations? Thank you

We got ours from this company - not sure how far they'll travel but we are London area and they are based in Suffolk:

www.ballantinesblinds.co.uk/products/specialist-blinds

Sorry, should have said that they came out to us to measure up and then came back to fit a few weeks later.