A swim ladder is always a good idea. I went even cheaper for my Oday 23:
http://www.westmarine.com/webapp/wc...toreNum=50304&subdeptNum=50353&classNum=50354
Buy a ladder with the "wide hooks" and the extra long standoffs to match the curve of the hull. The hooks fit over the gunwhales at the aft end of the cockpit. Before leaving the boat, I lash one hook to the stern pushpit so it can't come off. The ladder fits in the cockpit storage locker with no trouble.
Of course, this option has some drawbacks: it is not at the ready in case of a man overboard; you have to fish it out of the locker and attach it, and to make it really easy to use, you have to detach the lifeline. And it is of no safety value at all if you are singlehanding and fall overboard. On the other hand, it has the virtues of being cheap, and in my humble opinion, easier to use than a stern mounted set up. Any ladder you mount on the transom will require a swimmer to climb over the push pit (stern railing). Maybe easy for the boys, but not something the girls will relish. And the portable ladder does avoid the hassles of mounting something on the Oday 23 transom. If your 23 is like mine, the "open" side of the transom (i.e., the side where the interior of the transom is accessable through the inside of the cockpit locker) is already taken up with the outboard mount. Accessing the other side will require installation of at least one inspection port in order to get at the inside of the transom. Plus, you lose the ability to put your boat's name on the transom! Not a big deal for some people, but I greatly prefer the look of the name on the transom rather than the side.