There is no stated minimum. If you wish to participate, you can contact the WEL office and have them email you a pdf file to print. You fill in pertinent pages and send it back to them with a cheque. [I could also forward a copy of the pdf file - if you would like me to do that, send me a private message with your email address].
Note that you need to be an "accredited investor" to participate - that means you have a financial assets of over $1,000,000 or that you have income of $200,000 per year ($300,000 together with spouse), or a few other similar criteria (it is in the pdf). So not everyone will be in a position to take part.
NL