I am not sure what you mean by "a link to a virtual tour." If you are asking what they cost to have done, it really depends on how many images you would like to be presented but a good ballpark would be around $100.
Check out http://www.obeo.com
for more information. There are also many other companies out there as well.
If you meant something other than what does it cost to have a virtual tour done on your house, by all means post back and correct me so that I can be of further assistance.