You could always do that, although if you decide to have a veggie garden in the available garden space having your own bin would be very advantageous. Also, composting on site means less stuff in your recycle bin, athough 40 gallons is pretty big if you compact stuff before throwing it in.

I spent around $70 on my worm bin, its really nifty, although you could build one out of scavenged pallet lumber for (almost) free. And the contained worm-bin ones are pretty vermin-free... well, except for the worms that is. But yeah, if you decide to go that route let me know & i'll bring you some wormies. (Molly would probably LOVE feeding the worms...)