Good luck with your venture, it's tough. I've tried it.
The distributors charge different prices. The best thing to do is find the one closest to you to save on shipping costs. You can also try to buy direct from the companies but they do have guidelines you must follow.
Please do a careful market survey before you jump in. Most of these types of businesses fail very soon after they open. Remember, you are competing with ePay and the rest of the internet. Are you sure there are enough local people that will walk in your store and give you their money month after month, year after year? If not, be careful.
jdk...I think PWSchuh is 100% on mark. Brick and Mortar businesses that deal in diecast collectables not only compete with the internet but also the big box stores that get a huge wholesale price advantage. I believe most big box stores carry HW mainline as a loss leader... good luck either way.