Down on Myself

Today looks like another "down on myself" day.  I found a really great job that I am not really qualified for but the job posting doesn't require much so I am going to apply anyway.  It pays enough to allow me to stay in Chicago comfortably for sure.  And it is only 10 minutes from my house as opposed to my current job which is 60 minutes away.  Its taking me forever to apply because I'm struggling with the cover letter.  I know that the cover letter is going to be really important for me because I lack in knowledge.  But there is another position for the same company that pays 10K less, damn near what I am making now...but I know I could get that job.  I cant apply for both, I think that may be tacky.  So I have to choose whether to aim big or aim reasonable.  I don't know what to do...