We are developing a new financial portal, down the line our expected user for the portal is 20K. I believe the licenses for the 20 Vuser in LR will cost huge money, I want to find out any strategy or method be adopted to apply the load test with 20 users
You could choose to go with a combination of tools. In such a set up you could simulate the "easy" pages with for instance OPENSTA and go for large number of users and use LR to script the more tricky parts of the AUT.
This could potentially cut down on the number licenses you would need.
Will you really have 20,000 concurrent users? We have over 400,000 registered users on our site, but only have 200-250 active at any one time. We run our tests with 300 virtual users.
I would suggest you work with your business users/marketing/sales and determine what the real load is expected to be. If this still turns out to be prohibitively large, Roland's advice is a very good idea.