I think that there is a little more to it than that. You can get the permit for around $150.00 for the year but that is to do the bulk mailings and you have to have them sorted +4, into carrier routes, not just by zipcodes or streets.
It is a lot of work if you have not done it before but it can be learned.
I would wait until your marketing starts getting you calls, sometimes the marketing pieces do not do that good so you end up changing them.
That is why I have not done any mailers in a while, have not got the good marketing message that gets good results, when I get that then I will start again.
Go by or call the post office, they will explain the permit and how you have to do the cards for the cheaper rate, if you are not doing 1000's or more, I would not even look into it but that is me, I like to keep it simple for some things.