It's a train from Edinburgh to Birmingham (5 to 7 Pounds one way) and a bus from Birmingham to Bristol (1 to 8 Pounds one way), you can book both through their website. Then it's just a regular off-peak day return train ticket (9 Pounds) from Bristol to Bridgwater, from any of the normal train websites. You have to be a bit flexible with your schedule, because these Edinburgh-Birmingham train fares are only for some days of the week and only for one train per day. Also, I will have to stay in Birmingham for 2 nights, but I'll probably Couchsurf, and this way I will have some time to explore Bristol.