EIN is Employer identification number, you can get it if you register a business.
as long you get fictitious business name and pay annual business tax you can apply for EIN.
not sure your location but here in California city I am - I pay $150/year for business tax, plus of course regular income tax "from profit" but it is common practice for new businesses not to make any profit for 5 years.

. As a business you also can deduct many expenses you can not as individual.
you do not have to incorporate to get EIN, as simple sole proprietor you can get EIN, even if you DBA ( do business as ) John Smith- your name.
Even I am in California I will not pay $800 a year but have LLC in Nevada, it is $120 or $150 or so. Plus Nevada has some very nice legal loopholes, protections and is Business oriented

. Delaware comes up in discussions as well.
You also have to get registered agent,which will vary but usually around $100 a year or so.
so you do not have to incorporate in the state you are in. But theoretically if you operate (physically conduct business) from any state you either need to incorporate there or incorporate in other state and get foreign/out of state entity.
Lets say you incorporate in Utah as John's jeans and sell jeans to Utah clothing stores, now you want to sell jeans in California, you need to ask permission from California to sell jeans under the name John's Jeans. That could be as bad as incorporating in CA.
Assuming this is internet related, you should have no problems being registered in single location, there are many loopholes.
Getting incorporated is basically,as stated above, a way of forming a separate entity which gives you legal protection and personal assets protection. You business becomes liable, not you. Of course that is in a nutshell, devil lies in fine print.
Getting EIN, even as sole proprietor is a good decision especially helping you get business accounts and separating personal from business finances. Sole proprietor EIN is still linked to your SSN as far the IRS is concerned but you do not need to provide SSN to affl. networks etc. Sole proprietor is personally are liable for the business.
for your situation I think registering a business in your city as sole proprietor and maybe getting a mail box (not P.O) is good decision. You may decide later down the line to incorporate.
hope this helped a bit,
disclaimer

,
I am not a legal representative, so please do your own research and consult a legal council.
good luck