Alan wrote: And while it is true that the departents of Amazonas and Loreto are IGV 18% exonerated.
The only way to leave Iquitos is by boat so you will be charged tax because documents are checked before you enter the boat and you will still have to pay the tax.
I had a Hondas and Yamahas whilst living in Peru. They prices don't differ a lot. Only the dealers of the cheaper less reliable Chinese motorbikes like Zhongsheng, Lifan, Wanxin might negotiate the price.
But Honda and Yamaha generally have fixed prices. I recommend to buy them at a main dealer. Better service and free maintenance. They only charge for the parts that aren't covered by the guarantee and don't charge for working hours if you bike is still under guarantee.