Challenge - 7000 BTU Portable Air Conditioner (MPPH-07CRN7-QB6G1, MPPHA-07CRN7-QB6)

Pretty much all of the budget (350-800) portable AC units sold in the UK are single hose, because apparently we don't understand fluid dynamics here. If you buy one, make sure you can DIY convert it to dual hose to get any kind of decent performance out of it (see: https://www.woolie.co.uk/article/convert-ac-from-single-hose-to-dual-hose/) Then buy a £10 velcro adapter from amazon for your windows to get a good seal, especially if they're the outward opening variety. I have an inexpensive 7000BTU Challenge unit from Argos which converted nicely with a shoebox, some 6" duct, and some duct tape. It keeps a medium sized room about 22C when it's 30 outside (before the mod, it was useless.)

I brought an Argos Challenger unit around 5 years ago at the height of Summer for under £200. I'd been threatening to do it for years and snapped one day. I might have got it for less off season but the relief was almost instant. It still runs well so worth the investment. In the summer it lives in my bedroom but I only really use it when it's 28c and up. I only use it in the bedroom as it's smaller to cool and easier to use the hose. It's less expensive to run than my electric heating is over the winter. I've spent less than a £1 running it for 6-8 hours today.  The downside is it's LOUD. No escaping that