I've edited or co-edited three writers' group anthologies.
Firstly, I would be very clear as to whether this project is intended primarily as a souvenir for your group, or if you intend to potentially sell the book outside it. This will be reflected in the number of copies you print. The first one I was involved in had 200 copies. That proved to be too many, so the other two had 100 each. Nowadays, with print-on-demand you can print extra copies when needed instead of committing to a larger print run.
Don't expect to sell huge numbers to outsiders who aren't friends or relatives. Many of your would-be readers (of short fiction - not so sure about poetry) are would-be writers. It's hard to sell something to writers that they wouldn't be able to submit to later, as you would with a magazine or a semi-regular anthology series.
If you want to sell your book more widely than privately, you will need an ISBN - and I understand they are chargeable nowadays. (You're not obliged to have an ISBN, but people will need one to order your book unless directly from yourself.) You will also need six copies to send to the copyright libraries. Along with review copies, contributor copies and other free copies, these are things you will have to include in your budget.
Don't skimp on time for copy-editing, as nothing looks more amateurish than typos galore, or conventions on spelling (-ise or -ize?) and punctuation (single or double quote marks?) changing from one story to the next.
You might want to consider separating out publishing and marketing. I found that by the time the book was in my hand I was burned out from copy-editing, preparing it for typesetting and printing etc (and all the last-minute crises that come up). At that point it can be useful to have someone fresh to take over at that point and sell the finished product.
See if you can get the book reviewed. The Fix and Laura Hird's site are two online places that might review your book. Put together a press release and send it (and a copy of the book) to your local newspapers. If you're REALLY aiming high, send copies to the national press...and if you know a journalist, send one to him or her individually as well. (The Guardian occasionally reviews small-press books in its Saturday review section - I can't speak for other papers.)
Organise a book launch which needn't be elaborate - you can hire a room in your local pub if you like. But it's nice to have a party.
Anyway, best of luck!
