Short answer: depends on a number of factors.
Very long answer:
From Specsavers, standard monthly lenses (the ones you resuse every day for a month) are about £8 a month.
The ones you leave in 24/7 for a month are around £15.
I think dailies are also around £15 a month.
If you have an astigmatism (eye condition), you'll have to have toric lenses which cost slightly more.
Depends what you want lenses to do for you. If you want to wear them every day you're probably better off with monthlies or 24/7s.
If you're on the move a lot or only want to wear lenses occasionally, dailies are probably better for you as you throw them away at the end of each day, and don't have to worry about cases, solutions and suchlike.
Go to Specsavers....they're the cheapest!
Hope this helps!!