Iquitos is a wonderful place to go!
Iquitos is effectively land-locked by the surrounding Amazon jungle and the best transport is by plane or by boat, actually some say there is no other transport but someone did mention a bus.
I read about that bus from Lima but takes about 6 days in total and doesnt save you enough money to be worth it.
As far as I know the boat option is not really practical. By Plane the flight time from Lima to Iquitos is about 1 hour 15 minutes, and is about 627 miles (1,009 Km) by air.
There are several morning flights per day in both directions.
The price from Lima to Iquitos is $88.00 to $116.00 dollars depending on the airline and time of year. The airlines are Aerocondor, Lan Peru, and Star Peru, I would get that booked before arriving there if I were you.
Travellers should take medical advice at least three weeks before travelling there. Not sure how much money you should take it all depends on what you will be doing there.
You can check this links:
Flights to Peru,
Travel Insurance for Peru Peru Travel Tips
Be particularly careful with your valuables at any of the bus stations since there are always thieves and bag snatchers looking out for an opportunity.
I hope this helps!
Have fun.