According to The Making of Star Trek: The Motion Picture, the model of the Enterprise cost around $150,000 to make. In today's dollars, that's $530,000. So, wanting to make a replica of the TMP Enterprise wouldn't be cheap. But if it can be done for that or even a little more (and today it might even be done cheaper with newer technology), it seems hard to justify another $2.5 million in what would essentially be administrative costs.
There are also some important questions left unanswered in the pitch:
-- will the new company that will be formed be non-profit or for profit?
-- what happens to any equipment, supplies, and other items bought with donations when the project ends?
-- who will own the model?
-- will it be donated to a place like the Smithsonian?
-- will it go on tour for display and not have a permanent home?
-- will it be on display for free?
-- what happens to donations if the project is underfunded and can't be launched?
-- what happens if the project needs more money to continue or it will stop short?
-- what happens to donations if the project comes in under budget?
I'd need to have all those questions and probably some others answered before I even gave a nickel.
Edited to add: the model wouldn't be a "treasured artifact," it would be a newly made replica. If having a true "artifact" is so important, then try to find out who owns the original model, see how much the person would be willing to sell it for (everyone has a price), and try to spearhead a movement to raise that money. Then when it's bought through all the fan donations, give it to the Smithsonian or a similar place on the stipulation that it must go on periodic public tours so as many fans as possible get a chance to see it. Then, everyone gets the real thing.
