aahh, the memories! I have just got my bike out of Callao (well start of June anyway) and would not recommend this process to anyone. That advice of course will not help you now!
$590, whether you think it fair or not, is around the price you will have to pay. I did it myself, ie not through a broker, and ended up paying around $650, there will be some hidden costs before you finish.
I feel that $1900 is too much. To my knowledge there are only two wherehouses in Callao, DP World and Neptunia (this was mine). I dealt with them direct after paying the necessary charges to the local agent nominated by my Australian shipper. See if you can deal direct with the warehouse but you WILL need your bill of lading stamped by the importing agent (this will cost you money but my guy tried to automatically assume that I wanted them to act as my broker) Maybe this is happening to you. Just ask to pay the absolute minimum to get your BOL back with the correct stamp on it.
Apart from the cash for me it was the aduana that gave me 5 days of needless frustration. Make sure you have your paperwork in order before you submit it. I think there is a page on their web site with a full list of the paper required. One of which is a notarized letter stating what you want to do and copies of almost every document you submit, they will send you away time and time again until you are ready to head butt the bastards. The guy you will need to deal with is Saul, a real wanker based out of window 43 (at least I think that was the window). Take a big fat book and a bag of patience with these guys. Other wise, pay someone to do it and cop the financial beating.
Also I was not asked for any SOAT at any point even though I had purchased it (you will need it anyway) I looked everywhere for a months worth as everyone wanted to sell me a full year. Go to MAPFRE near Miraflores and save your self the run around. Costs 67s/
Callao is a dodgy area, keep yourself aware. There is better transport to the port from Lima central than Miraflores and you will have to carry cash on you. Aduana is open from around 8:30, get there early and enjoy the franticness. Go straight to counter 43 and get the party started. They dont speak english and my spanish is not good = added frustration.
There is not much you can really do until the bike actually arrives. There is a good post on here from a german guy with clear details of how to navigate the challenges. If you have any questions then PM me and .....
....... GOOD LUCK
ps - headbutt Saul for me!