$25 seems little money for a professional map, though perhaps someone very "amateurish" (like me, but not me because I can't really draw either) could do that for that pittance.
However, there is a big difference between offering money in payment and organizing a "lottery" for the same "prize". You are basically asking people to do the work for free, on the chance, the mere chance, of winning the (little) prize you are offering... I can't see anyone who is able to do maps remotely as good as those you have as examples in your blog taking such a chance.
You would probably have a better chance of success by offering the money outright and see if someone is interested, and choose based on his or her previous work.

On an unrelated note, "A Dance of Dragons" is a weird choice for a title these days, given how similar it is to the last volume of one of the most famous fantasy series of all time (one which you even CITE in the very description of your own work!), which also happens to have been published fairly recently.