I was contemplating a writing slope and have been looking at them on eBay but then came across Rutland Woodcraft here. I wrote to them about their writing slopes and got the following response: -

Basically there are four options for you. One would be to have a box made
to a similar specification as the walnut one on the website for around
£1250. The second would be to purchase the box shown in the attached
pictures for £500.This could also have more things added to it inside such
as drawers or dividers etc at cost.Third you may like to purchase one of the
nelson’s writing boxes see the nelson’s victory page on the website for
£2245.Finally you may like to have one made to commission for approximately
£950 to thousands of pounds depending on it’s complexity.
Once again thank you for your enquiry and do get in touch if any of these
options appeal to you.

The attached picture shows a sloped wooden box which is empty inside.

The cost is outside my budget, but I know that some here are not in the impoverished league so thought that I might bring it to your attention. If you can afford two I am always happy to receive one!