How much do you want to spend? I assume that you want a real translation, not to just drop your INDDs into some kind of software and get a machine-produced document out the other side. I might be wrong on that account; if so, let me know, and I promise to only spend a few minutes telling you what a terrible idea that is, before I give you some pointers on how to get it done.
But, assuming that you don't want a purely AI-driven workflow: pretty much any languages service provider worth its salt can work directly on IDML files that you can export from InDesign. Most of them will offer to do post-translation cleanup in InDesign - which will be necessary, as you can expect the Spanish text to have a character count that is at least 10%-20% higher than the English - for an additional hourly fee. If you feel confident in your Spanish literacy, then you might want to skip on the DTP services and do it yourself. If you go that route, you're probably going to want to ask your provider for a post-formatting review of the final book.
Most of these potential providers will use a combination of human translators and machine translation.
Most of these language service providers will have some area of focus, be that on tech translation or marketing or life sciences, et cetera. So picking a provider that matches the subject area of your book will probably be important.