It can take 10 - 20 minutes into town in a taxi - longer at busy times. It costs roughly £20-30 due to the fact we are actually in South Gloucestershire and not Bristol.
As stated in previous answers it can be quicker to go the longer route via the M32 at the busier times however the longer distance also equals a significant increase in price for a taxi.
There are regular buses from across the road which cost £4.40 for a day rider or £3.50 single way. They run every 10 minutes and take about 40 minutes.