A possible reason of why the 50mm will look like its taking better pictures is likely because its a much wider aperture than the 18-55mm. (f1.8 versus f3.5 (or whatever)) As a result, its able to allow a lot more light to come through the lens and hit the sensor. In turn, because it has more light coming in, the camera can use a lower sensitivity setting (ISO) whilst still being able to record a good quality picture. A benefit as mentioned already is that you get a better depth of field look to the pictures as well.
In general terms, the lower the ISO value, the smoother the noise of the image will be. This is particularly noticeable when shooting in low light situations, such as bedrooms and hotel rooms. If your pictures looking grainy and noisy, then the camera is likely having to turn up the ISO sensitivity as its wanting more light.
There are 2 ways to try and counter the low light.
1: Have lenses which have wide apertures ( or low value f-numbers like f1.4, f.2 etc ). Whilst the nifty 50mm lens has this and is cheap, its just about the only one that is that cheap. Wider apertures = more glass = more cost. Lenses which have a zoom feature have more parts to the lenses so are even more expensive. This is why the low f-number lens tend to be primes (fixed focal length) to save cost.
2: Add more light. You'll no doubt have seen that many photoshoots, bloggers, only fan creators etc will have lights all about the place ... the reason being that by adding more light to the scene, you're letting more into the camera and so the picture quality may improve. Just like lenses, lighting is a huge subject.
I wouldn't recommend the 10-22 type lenses ... they are so wide that you start to get distortion of the subject. You're subject will look odd. Kenai is right with his recommendation of trying the 18-55 more and seeing what focal length suits and then take it from there.
The closest thing to matching your nifty 50 in your price range would be the EF-S 24mm prime lens. (~£150). Its fairly wide angle compared to the 50. Its f2.8 so will let more light in that the 18-55 lens you have ( but not as much as the 50 ), so should give better results.
Before you commit to that though, set the 18-55 to 24mm and leave it there, then only take shots at that focal length and see what you think. If that suits in terms of getting what you want as an overall picture, then maybe worth buying that lens for its better low light performance.
Also the Sigma 17-50 f2.8 is a good shout ... same aperture as the 24, but has zoom ability. On ebay there area couple of Canon fit lens for sale at the moment with Buy it Now of ~£220, which I would say looks a good deal. (search for "Sigma EX HSM OS DC 17 50mm F/2.8 Lens for Canon" and they should appear)
At the same time, experiment with lighting. Add more lights to the room. A single angle-poise light with a bright bulb in it shone up at the ceiling or against a wall behind the camera will add a ton more diffuse light to a room and may improve the pictures more as well.
Lastly, take your time ... compose the shots, if the subject goes out of frame, tell them ... nicely.
