Hey Pete,
Newsletters are a great way to keep in touch with your customers, we send them out every 2 months (single side full colour- funky & too the point) and get a great return in the summer months. All our newsletters and leaflets are created in-house using various software & techniques, and can be extremely time consuming if you don't know what your doing!
Many people use the generic fastrack newsletters, which are great, just too many going out in my area! If they are not an option, or just not the approach you are going for then designing you own is the obvious option, although expect alot of trial & error it takes time to plan, and measure each mail out to get the desired or acceptable level of return. That being the cheaper option (although if you count the time you spend in front of your pc maybe not) Commisioning someone else to to all the work for you could be beneficial if you don't mind spending £100 ish plus printing. We use printroom-online.co.uk -13p- 19p per sheet, next day delivery and great finish.
Look at newsletters from other trades if you can (just not your rival cc!), even emails from company's, find and note down anything that gets you thinking, or that grabs your attention, and try and work the core values and ideas into your own. Remember, just because it looks good to you, it doesn't mean your prospective customer will agree!
Happy designing!