my 2 cents. Extra Mods should be generally free, but come with an ad link of the creator, like you guys did with the whole script. This would give people time to test a mod if it works as promised and then to buy a link free mod or simply forget about it. This then could determine the level of trust in a mod creator. Joomla extension is a good example. Most mods are free, many come with an ad link for free but are fully functional and some, - those with the lowest sales come with a price tag and see more without a chance of testing.
I also realize that extensions at Joomla are reasonably priced. Why not take it as an example?