The cheapest way unless you have the cash will more than likely be to release some equity in your home - or one of your homes if you have several - and get the cash.
But I would agree with Mono; if you are taking out any sort of finance to buy a plane, you should look on it as a business and set up a proper business plan and aim for some profit. If the profit isn't there, you may want to rethink doing it...
If it flies, f#¤&s or floats...
B.