Apus is the European market name for the UMAX SuperMac family, so this is a C500/180, which is a fine little computer. It's basically gonna perform like a 6400/180, perhaps a little better than some /180s if it has an L2 cache (euro-market 6400s in particular sometimes didn't) and it doesn't have the a/v stuff the 6400 did. I don't remember hearing anything weird about the architecture here, so you might get a little more flexibility with internal upgrades, but, a 7/8/9-series competitor, this isn't, regardless.
In general, a clone will fetch a little bit more than the Apple version of a system, by virtue of being a little less common and in some cases, being better built or having less nonsense.
W/re the CD-ROM drive price: Sure, but, this isn't a SCSI CD-ROM drive on its own, it's a system.
W/re this being the wrong place for a valuation: "eeh". I'm not going to say somebody isn't allowed to ask, but it's not something you'll likely find a favorable answer on here, because the people are are motivated by getting a good deal. If that's fine and you want to send this into a good home, or you're pricing out things for, some kind of insurance, well, just be aware that none (? as far as I know) are "professionals" at this stuff.
In terms of eBay completed listing values. Those are often wrong. I forget which direction, but eBay doesn't show the correct completed price for items, so it's good for an idea but not necessarily good for what people are actually paying. The other problem is, that, as mentioned above, the clones in particular aren't always on eBay and so it's tough to tell what one might sell for today.
That said: What joethezombie mentioned, approximately $115, is about what I'd really expect. (That's roughly 90 UK Pounds)Maybe a little higher if you have a good L2 cache or a fair amount of RAM or a replacement disk drive or ethernet installed and it became a little bit of a getting started kit for someone who might wanted to get started with the hobby.
As a comparison, there are a handful of Macintosh 6360 models on US eBay for around $55-400 in varying configs, although that most expensive example has been around for several months. Most of those are listed above what I'd be interested in paying for a 6360, although the one at $300 is the only one that's shown to be booting, where (most of) the configuration is listed, includes a keyboard, mouse, and a reasonably good monitor. Still kind of high though, but perhaps worth it to someone who just wants something that works to put oregon trail and hypercard on. (Though, as mentioned, it doesn't appear to have proven itself as such yet.)