One method you might consider is the pando (one big tree) at WeRelate.org. It's free and run by a foundation, not a for-profit corporation. It's a pando of sources and places as well as of people. You could look up if your town was already present (e.g. Scituate, MA) and then see what links there (e.g. all the people with links to that place) by clicking on the sidebar. Or you could make your own 'template' and link the early founders together. You can also include a link to your society on that page (and on this one too!).
You might also look at how other local societies did it. For example, I grew up in Scituate, Mass and you can see their website has a section with the early families.
As an example of how existing software can be used (albeit for a slightly different purpose but it's illustrative for your needs), I used this site to derive which of my ancestors are descended from these early families. I found I was descended from 9 of the 40 (not many choices in the early years so lots of intermarriage among those 40 families). I made some descendant charts by making a temporary gedcom and then creating a mythical person called Scituate. I had each of the 9 have Scituate as their father. Then using Gramps (a free open-source genealogy program), I made a graphviz (a free open-source graphing program) descendant chart which I then trimmed the graphviz source (eg remove the other descendants, made the line to 'Scituate' invisible for each of the founders, etc). I could have done most of the trimming in gramps but doing it in graphviz then me do things like make the fake lines invisible.
I'd also suggest you include the name of your town in your question. This will allow people doing google searches to find this question on this site. You can also use specific questions (e.g. about a given founder) on this site to draw interest - and get answers! I.e. genealogy.se can be a 'free' site for you also, as long as you use it as it was intended. You might find there is a lot more interest in your small town than you realized and se can help you leverage that interest.