I studied with the OU in the 1990s and was able to use my credits in lieu of qualifications for full time university. After I'd graduated, I went back to the OU to get Diploma in Music and I'm now on my way to a second degree.
The range of courses on offer now is astounding, with a wide variety of short and taster courses to get you started. They start at around the �120 mark, but you can pay on a month by month basis and as pastafreak says, benefits may entitle you to some fee remission.
Traditional universities will require you to take, as a minimum, one of their access courses, which can often be virtually full time and with very little financial support.
Also, if you decide to take a full time university course, then your benefits could well be affected. Whereas taking OU courses won't affect your benefits at all.
Good luck.