I'm not sure that the one-way thing is any sort of shield.  Jewellers, for instance, are subject to AML regulations based on their volume of business even if they do not buy from the general public.  

It's also worth noting that the IRS itself carries out AML investigations and makes referrals to FinCEN - merely paying your taxes is not enough to protect you if you're required to comply with AML regulations and fail to do so.

There may be some exemptions open to you if you operate within certain limits.  It's worth seeking advice from an experienced financial services lawyer to find out in what circumstances exemptions might apply.  Operating within those limits might be more financially viable for you at this time than seeking licensing.  Obtaining an exemption is a formal process - you have to apply for it so it still costs money.