You could post a request or contact translators directly. However, unless it's a very popular and new movie, I think chances are pretty low, since there are zillion of people wanting subs for this or that movie and only a few translators. (Btw, please DO NOT post your request in this forum - for the same reason, this forum would be flooded and rendered useless.)
You could try to find the movie on DVD or Bluray with the Spanish subtitles and rip the subtitles from that disk. It may be worth it to check if a torrent of the video file with embedded subs exists.
You could try your idea with Youtube. Upload the movie, and use their speech recognition system to generate the subtitles. Keep in mind that most probably the result will be far from perfect and needing some or a lot of corrections.
Or, if you just need a rough written meaning of the text (instead of the exact literal transcript), you could try taking any existing subtitle in any language and let Google translate it. I think best results are using English as source, but same same as with Youtube, this will still be poor quality and needing a lot of manual corrections.
I wouldn't know about paid subtitlers. The OpenSubtitles community is crowded with non-paid volunteers doing their hobby. You would need to find a professional. Keep in mind that this will not be cheap. Depending on the length and complexity of the movie, making subtitles takes roughly 10-20 hours. Multiply that by an average hour salary.