England & Scotland LOW COST

Next Friday I'm flying to London. Once landed at Stansted airport (with Ryanair, obviously :S) I am going to take the Megabus to Edinburgh - a long, whole night journey.

I was wondering how can be something that amazing as a day guided tour in the Highlands FREE!
Browsing the web I encountered the Hairy Coo Highlands tour, that starts every day from Edinburgh... Total price: 0,00 GBP!!!

My goal is to spend less than 120 euros for a 4-5 day trip to London, Edinburgh and the Highlands.