Hi, I can try to help you, if you want, with a partial work. I will not say "I am great in Spanish", because I'm not, but I checked the preview of your book and working in marketing I know that I would be able to translate it, slowly and using the dictionary carefully.
Why did I say partially? I'm a perfectionist, I had to grant you the work only if Spanish had to be a language that I deeply studied and daily used, and that's not the case, so the translation will have some imperfections (mostly in common sayings). So, to have a perfect work you will need a proofread.
Which are pros? Well, I will need more time but I will ask less money. Plus I'm Italian and, as you can check on yourself, Italian people are really interested in these type of books, so if you would like I could translate also in Italian (in this case absolutely no proofread needed, I will just need that you will mark me common sayings so that i would be able to properly substitute them with Italyan common sayings).
About price and time? Well, if you want you can contact me and you can propose it. As "random" propose atm I would say $250 and 56 days (as I said I would go slow to provide an almost perfect translation, but if you want to hurry, just say it, we can manage it), if you would like to add an Italian one, if it will be at the same time, I would ask $150 and probably neither one week extra (I would translate in both languages at the same time).
Strange propose but I'm transparent.
Best Regards