Get the Harbor Freight support bar for $48 with the 20% off coupon. There is one is this months Car and Driver, if you are not on Harbor Freights mailing list. I went to get mine today, but they were out of them at the store I went to. They have 5 in stock on the other side of town, so I will be going there tomorrow.
You will probably spend more than $50 in lumber for your wood frame deal. The support bar is a better method than jacking up the engine by the oil pan, IMO. I know you like to save some money, but this is about safety and what is best for your car. You will be kicking yourself if something happens to your oil pan if you jack it up, and you don't want to get squashed under a home made engine lift, that is a bad way to go.