I see from your profile that you're based in Warrington. What type of user group were you looking for .NET, Java, SQL ... general? There's a nice group in Manchester that you might be interested in: http://www.nxtgenug.net/Region.aspx?RegionID=11
In my experience, user groups derive their focus out of what the co-ordinator (or group of co-ordinators) is interested in. For example, if you are big into Silverlight then your own group would probably have that bias. Similarly, if your focus is more to network with other local devs just to chat, maybe code a little, talk about jobs and share experiences, then you will find that people with similar persuasions will join you. After all, there is not much point to a group where the people attending are not interested in the information that they get from the group :)
Depending on what it is that you are looking to get out of spending time with other devs will determine whether you want your group to be an educational group or a networking group. Groups like London's Silverlight user group, London .NET and the regional NxtGen User Groups focus more on education and sharing knowledge. They invite a monthly speaker to come and share their specialities with the group. On the other hand "meetups" (I think there is a fledgling one in Cambridge) have a more social aspect where the attendees participate more to spend leisure time after work with like-minded people rather than to necessarily "learn about" new stuff.
If you haven't yet got a feel for what you want your group to focus on, maybe you could arrange an informal meetup to see what others in your area are interested in - educational talks or networking - that may help to determine the expectations of your potential attendees and formulate the best plan.
Depending on what type of group you have, there are a lot of places that you can promote your group or meetup. Microsoft operate a list that includes UK events in its Flash newsletter. Twitter is a great way to promote your group, since people in the UK community share links and events like wildfire. You might also try promoting it to local companies that you know have an IT/development department, maybe a printed flyer or a quick call to the company to get the email address of someone who might be interested enough to share the group information with their colleagues. I would offer this advice: don't be put off if you don't get great traction right away. We have a .NET user group in Cambridge and it has taken us a long time (almost 4 years, I think) to get a regular turn out of 30-40 each month. The success and benefits of your group will depend on your commitment to keep pushing on through even if you think you're not getting anywhere.
As to the financial side of things, the single biggest pain in the butt is finding a venue who will allow you to make a regular arrangement to hold your meeting there. If you plan to do more of the networking thing, this might not pose such a problem for you as you can arrange to meet at a pub or coffee house where you can usually ask to reserve a little bit of space for no fee. If you are going for the regular education meeting style approach, try asking your company if they might let you have a room in your building one night each month to hold it. Regularity and consistency is one of the keys to hosting a successful educational user group.
If you want to organise food and drinks for your attendees, you should try seeking out vendor support from organisations who offer products/services in the field that you are interested in. For example, I help with the Cambridge NxtGen group and I also work for DevExpress. NxtGen is a Microsoft technology focused group for the main part, and DevExpress offer products in this area. NxtGen reached out to us and other vendors like Red Gate, JetBrains, Pluralsight for support in the form of money to pay for pizza and also prizes for monthly raffles to entice more attendees into the group (if they know that they can win valuable stuff and pick up things like shirts and trinkets then it might make them think favourably about coming to your group every time you host a meeting). If you know of vendors who operate in the area that you are interested in then try the same approach and see what they say. I have mostly found .NET vendors to be very forthcoming with their support, so I can't imagine why vendors in other areas might not work the same way.
I'd be happy to link you with other user group leaders who can offer you advice. You can find me on Twitter (@RachelHawley) and you can email me at rachelh at the DevExpress domain.