There's nothing prohibiting you from including a [COLOR=#404040]PayPal payment subscription[/COLOR] button somewhere in your theme. The difficult part is managing the subscriptions, which is what you get when you buy the Woo plugin. If you believe you can do it all manually and that the time it takes is worth less than $ 200 in the long run, go ahead and do it.
Otherwise, buy the darn plugin and spare yourself a lot of time and trouble. The price is really not that costly when you consider what you get and how much it would cost to build it on your own.