That's at least £150 less than the most comparable Nokia, the £360. We haven't reviewed the 8S yet, so I can't say exactly how they stack up, but let's have a look at what you get on paper.
The 8S has a slightly smaller screen than the 820 -- 4 inches versus 4.3 inches -- but the resolution is exactly the same, 480x800 pixels. That's not fantastic (the 4.7-inch Nexus 4, only £20 more, has 768x1,280 pixels) but it does mean the 8S has a few more pixels per inch than the 820, so in theory it'll be slightly sharper. The 820 has 217 pixels per inch, whereas the 8S has 233 (the Nexus 4 has a staggering 317).
Leaving the-toting Nexus 4 to one side, the 8S lacks . These are Nokia Drive, a turn-by-turn sat-nav app; Nokia CityLens, which overlays useful local information on your camera display; and Nokia Music, which streams tunes for free. All are well made and valuable, and make up somewhat for the lack of great apps on Windows Marketplace, but none are indispensable.
The real difference between the two phones is invisible: the components inside. The 820 has significantly more powerful chips, such as a 1.5GHz dual-core processor and 1GB of RAM, compared to the 8S's slower 1GHz chip and pathetic 512MB of RAM.
Whether you'll notice any difference is hard to say without using the 8S extensively and running benchmarks. But Windows Phone's transitions -- the animations that move you from one screen to the next -- run at a fixed pace. In theory, you'll only notice performance on games and other testing apps, of which there are few in the Marketplace right now.
Elsewhere, both take microSD cards to expand your storage up to 64GB. The Nokia's 8-megapixel camera trounces the HTC's 5-megapixel effort on paper at least, and I wouldn't be surprised for the difference to be marked in their photos. We found the 820's camera very good for what you're paying.
Compare phones on contract, pay as you go and SIM-free on our mobile deals section -- you'll find the HTC 8S and Nokia Lumia 820 at those links. Which of these Windows Phones floats your boat? Would you take a punt on either of them? Let me know down in the comments, or on our bargain-basement Facebook page.