I suggest you to take a look at the prices provided by the retailers in Find Retailers for Intel® Edison and Intel® Galileo Boards . You will see that different retailers have different prices so I recommend you to check those websites and look for the best option for you.
For the combo with the official Intel mini breakout board and an Edison module, I would say that the price is normally around the $75 (USD) mark, with small variations from store to store.
If you find it a lot cheaper (like the $55 you have mentioned), it's probably some sort of promotion, and if you see it a lot more expensive, my first guess is that it's not the exact same product. It could of course also be that someone tries to make an extra buck, but most likely it's a different breakout board or maybe more stuff included in a bundle (cables, battery, antenna, etc.). If it is the exact same, I would move on and find another place to buy it.