From the airport on foot:

There is a bus that runs between the airport and the city centre approximately every 15 minutes. The fare is about £3.60 one-way or about £6.00 return, the stop is at Waverley Bridge and a taxi from there would be another £5.00. It is walkable, but I usually wouldn't recommend it if your bags are heavy or if you are unsure of the location of the guest house. Alternatively, a taxi would cost from £15.00 - £17.00 from the airport direct to the guest house.