Bit late I know, but this caught my eye as I get asked it a lot so thought I'd chip in for anyone seeing it late too and wanting a quick answer!
VLE's tend to have 3 price structures:
1) Annual Fee Subscription
2) License Based Subscription
3) Combination of the above
1)Annual fees
Cost will generally be between £500 - £5000 depending on the school size and type. Some price by size, others by Primary, Middle or Secondary. I have worked on a number of non-school set-ups (for upto 50,000 users which will require a bespoke quote).
Typically there will also be some start up costs which include set up, integration, branding, training etc (you will be told that £3k is typical for a standard set up. If you have more complex integrations and/or server requirements this can drastically increase).
2) License based subscription.
Again, you will have associated start up costs. These should be the same as above.
A license can cost anywhere between £2 and £50, depending on how many users you have. It all evens out and you will generally find that the overall cost will be similar to that of the Annual Fee Subscription. I have found though that there is more scope for negotiation with these deals (ie first year trial basis etc).
3) Combination
A number of the larger companies will charge both of the above, but again it evens out to cost approximately the same.
So in a nutshell, some approximate prices (which are by no means concrete) for a standard set up are:
Secondary school with 2000 students - £3-5k set up. £5-6k per year.
Primary school with 100 students - £1k set up. £500 per year.
Having said that, it all depends on what you want it to do. If you want an all singing, all dancing system then it's more likely to be £10k set up and £20k per year. If you want it to do the basics, budget accordingly!