Smallest bottle of Heptavac is £20 or so and has 25 doses in it. You are supposed to discard any remaining vaccine so you'd need two bottles, if you follow the instructions to the letter (personally, I'd keep it sterile ie put one sterile needle in to draw off, then keep the bottle in the fridge for the second dose) or I'd see if there was anyone local who could give you a couple of doses. Or you might just want to risk it, for a couple of months.