After my booking was completed with RyanAir, I realized that I have to transfer from STN to LTN to complete my journey. I have used LHR and GAT numerous occasions but not either one of these. I have about 7 hours to transfer. Is it easy to do? I have found a few transfer companies with various rates. Is it recommended to buy ticket online in advance? Sometimes buying the ticket at the airport is cheaper because there is no middleman. All you are risking in this case is the shuttle seats maybe sold out, I think.

>> Sometimes buying the ticket at the airport is cheaper because there is no middleman. <<

Not sure I understand -- there is no 'middleman at the airport or in advance. National Express runs the coach service. Most of the time you save a little buying in advance. Stansted to Luton takes about 90 minutes but it only runs every hour. (all this info is easily found on-line)

A 'transfer service' would cost MUCH more than just taking the National Express regular service coach . . .

Yes it is easy to do, once you have found the bus station at Stansted and figured out which line to stand in to wait for your coach. The final destination of the coach service might not be Luton Airport, so take a note of the coach number so you don't miss it. I took a coach transfer once between LHR and STN and thought somehow that the destination on the front of the coach would be Stansted but it was some place in Norwich, Stansted was just a stop along the way. You can buy the tickets at the airport at the bus station but best to buy in advance to save time.

Book on this website and print your ticket.
https://www.nationalexpress.com/en

Thank you for your replies, Janis and Odin. I will buy my ticket online. What I meant by middleman was the website operator. When I needed to travel on ferries (Spain, Greece, Italy, etc), I found the website operators are the middlemen connecting passengers and ferry lines.

In the UK in transport the middle man is "scraping the tail" (tiny %) of the deal not the head of the deal (large %) themselves so even if there was a price difference it is hardly worth picking up.

Sometimes you can get cheaper National Express tickets if you book through another site, I noticed that after I had booked my coach tickets from LHR to STN. If I had booked thru the Ryanair website, it would have been less expensive. That may or may not be the case with your tickets but book in advance as it does become more expensive the closer you get to travel date.

Ryanair Airport Transfers