Debbie, Billy was stung a couple of weeks ago and although he was breathing okay so it obviously wasn't a bad reaction, he had a few swellings - including one on his lip - and was obviously uncomfortable. Googling it mostly recommended getting a vet appointment just to be on the safe side. A bit more Googling though revealed that human anti-histamine tablets can be given for stings, and I had a box in the cupboard which cost something like 79p for 14. I carefully checked the ingredients and the dosage, he had one and was much happier after a short while.
Oh, and last year he had a small patch of red skin on his leg. The vet prescribed a small tube of Fuciderm cream and along with the consultation it all cost around £60. The cream didn't fully clear up the patch, it kept coming back, so the tube got used up and I called for a repeat. I was told that because it was a steroid he'd need another consultation, so that'd obviously be another £60.
Google was my friend again. I had a small tub of Sudocrem in the cupboard and put a small smear of it on the red patch, the following day it was gone and has never returned!