You might well find that the cost for a couple of days isn't any less than that for a week or two. (I did a day's work trial for a skip hire company. It didn't matter whether the client wanted a skip on site for just one a day or for a full month; the price was exactly the same because it was the delivery and collection, together with the disposal of the contents, that was actually being charged for).
This firm, for instance, (which operates in the south-western corner of the country) charges £24 per week but with a minimal rental period of 2 weeks. Then you've got £19 each way to pay for delivery and collection on top of that, which brings the cost up to £86 per loo for a nominal 2-week hire. (They'd probably happily collect the loo after just 2 days but you'd still get clobbered for the full 2-week fee):
https://www.andyloos.co.uk/portable-toilet-hire-cost/