My idea is beyond this, but the basic gist is to create several stages. 'Alpha' 'Beta' 'Live' '10' '#'. So if a person is very interested or wants the finished product, etc, then there's a variety of matching options.
However it'd really depends on what the offer is. This is an indirect suggestion to do some marketing 101 ;)
I recently blogged an interesting approach by an app (called livepath) which let people buy into a beta account. Whenever the beta was a bit further developped he dropped the pricing a bit. Here's the link: http://blog.thegodfounder.com/post/5894377639/lifepaths-sign...
Minecraft creator took the inverse, charge more as software entered alpha to beta to gold. I suppose the high initial cost until normal cost makes sense in a reverse dutch auction if you got the hype.