I pay £122.9 in Tescos, but at the local 2 x private filling stations diesel is £125.9. It hasn't been lower than £121.9 for months, though did go up to £131.9 at its height. As a newbie I based my cashflow on that price last year when I started.
In the end it's going to go up as it's a finite resource.
As an aside we have an oil fired boiler/range that we inherited when we moved here in 2007. It does our DHW and CH. I fill up with a 1000 litres 4 or 5 times a year depending on how cold it's been. When we moved in we paid £339 for 1000 litres of oil; at the height of the oil prices it was £606 for a 100l; now its around £440. So, on £440 and filling up only 4 x a year we pay £1760 or £146 per month. A lot of people are complaining about their gas bills going up, and rightly too, but if you are paying less than £146 a month for gas consider yourself lucky. Our eleccy bill is £48 pm. We would change the boiler but it would mean a total revamp of the kitchen / plumbing as the range is the only source of heat in the kitchen.