Working the bill out first
Most of the anxiety around this job is not about language at all. It is about not knowing what the invoice will say. Per-page pricing takes that away, because the quantity is sitting on your desk already. Lay the record out, count the pages, multiply by £25, and you have a figure you can take to whoever is paying before a single line is written.
The language Sudan requires
Arabic is what is needed for documents used in Sudan, and the whole record goes across rather than the parts that look important. That matters to the budget as well as to the reader, because it is the reason the count is the count. Skipping a page of small print does not make the file cheaper in the end; it simply moves the cost from money to time.
Certification Sudan accepts
What arrives is Arabic accompanied by a signed, dated statement that the translation matches the record supplied, prepared by a certified Arabic translator. Consulates and ministries accept work certified this way, so the credential question is settled and does not become another variable in the price. Notarisation can be added if the body you are dealing with asks for it on top.
Per-page cost and turnaround
So the two numbers you need are easy to hold in your head: £25 for each page, and 3–5 business days from a clear image, or 48 hours if you take the express route. Neither figure moves with the destination or with how complicated the wording turns out to be. That is the point of quoting by the page rather than by the job.