The offering price is supposed to be the price, especially for reservationists. How long that price will remain in effect after production begins is not known.
UPDATE
As a refundable reservationist, you will receive your Elio after all the all-in reservationists have their cars. Currently, 85% of the reservations are all-in, and that will climb. So that puts you pretty far down the list. Going all-in now, even for $250, and signing the commitment statement, will lock in your price AND save you $300. So you help Elio, help yourself, and avoid a possible price increase.