For example, a company will sign up but their membership price will depend on how many employees they have, so:

Company with 1 – 10 employees will be charged ￡15 per employee per annum

Company with 11 – 20 employees will be charged ￡10 per employee per annum

Company with 21 – 30 employees will be charged ￡8 per employee per annum

etc…

I had been using memberpress but this doesn’t seem to have any functionality for the above.

Can anyone can point me in the direction of a plugin that could do this, or a work around for it?

Well supported and documented, and they’re always iterating and improving their products.

They could probably create something that will adjust dynamically to what you described, for e.g. user completes a form and based on input for # of employees the price will update.

Paid Membership Pro uses a number of payment gateways, including Stripe which I hear and read is great to develop with. I believe they also have a network of developers / partners they can refer who can assist with development also.