To Half or Not?

Last night I was all set to sign up for the Zooma Half marathon on Nov 16. Tried of thinking about it, just do it.Printed out the training plan, got up early and did my 45 minute "long run" and was feeling good, feeling strong. Got home and my right shin is aching, I pull up the registration form. What the...$75 to register? I am typically not a cheap person but $75 for something I not convinced isn't going to turn out to be painful. $75 can get me real close to a new pair of running shoes. Hummm. What to do? On Nov 16 would I find myself saying " I can't believe I paid $75 to do this"? I am pretty sure I wouldn't be saying "That's the best $75 I ever spent" What to do, what to do....

Did I mention that my shin has continued to ache all day. ( do I see a loop hole?)