Is it possible for SEO experts to do this?

[nastea]

On sites like getafreelancer.com or getacoder.com I've seen people asking the freelancers to put their web page in top 10 in Google for example. Is this possible?

How much time will your webpage stay there?

Why do prices differ so much? Some might ask less than $300 for this, others more than $3000.

I'm very confused. I want to invest, but I'm not sure I know what I\m doing.

[jewelking_2000]

It is possible to get to the top of niche markets quite easily for instance try silver wholesale jewellery in google and you will find http://www.wjsutton.co.uk well listed. If we tried to be well listed for jewelry we would have no chance. My advice is don't pay anyone for this do it yourself it isn't that difficult.
Some SEO cheat the system to get a short term listing which quickly evaporates. Get a book and diy, treat it as a game but niches only.