It's probably cheaper than weddings - but being serious, nobody can quote without knowing the project details. Most production companies work on a rigid £/hour basis (which means the quote will be drastically different from the real price once, the clients start making changes - or they do a price for the job, once they have an idea what it's about. Running time is also a big contributor to price. An eight minute video for web and presentation purposes might be five grand, or as cheap as five hundred. You will pay for quality, equipment, special effects and editing. For instance, a project designed for sales reps to play on an iPad in the clients premises might suddenly get a big price hike of the client suddenly wants a DVD - because authoring a DVD takes extra time, and very often an extra day or so.
What extra will cost? Music. The price to get copyright clearance depends on the medium and quantity. So a few DVDs won't be that expensive, but worldwide access on the web will be.
An alternative is library music that is music that is designed specifically for this kind of thing - instantly forgettable but ok. It's cheaper. Or, you could have music specially composed and recorded. Virtually all well known tunes on TV ads have been re-recorded, which means only the composer to pay, not the original artiste.
Sound on location. If you need location sound, it's an extra body to pay, and extra equipment, and of course extra edit time.
Graphics. Do you need complex graphics? As an example, in one we did, dirty linen went in one end of a machine, and came out clean the other end. Very dull, so we were asked to produce an animated graphic showing how it worked, and how the linen got clean. Took three whole days to produce 30 seconds of video.
If you want broadcast HD quality that looks professional, then the equipment is expensive, and possibly certain shots need specialist equipment, that will be hired in.
So to get an idea of the price, what have you got in mind?