As mentioned, you didn't list any requirements for things like screen size, communication / out, sailing area, etc.
For me personally, there is no way I would use a device like an IPAD. Things like water sealing, screen visibility (direct sunlight, twilight, and total darkness), connectivity, power, etc. are all very important to me. At a minimum, I want my GPS connected to my VHF for DSC mayday type signaling. I don't believe the IPAD would meet my needs.
I don't know where you got your pricing information, but you are way off. You can get a basic GPS system, with 5" color screen and detailed charts for under $400 (Standard Horizon CP 180). If you want a unit that could be upgraded to display RADAR, SONAR, video, you can get one for under $750 (Lowrance HDS 5).
IMHO, for a plotter to be useful:
- it must be mounted at the helm (and waterproof)
- It must run off of the boat's electrical system so the batteries won't be dead at an inopportune time
- GPS data can is sent to the ship DSC VHF radio
Imaging arriving at a new port with a tricky approach including a number of different bouys, shoals, and marine traffic. You arrive after a fairly long sail, say 8-10 hours. There are commercial ferry's and fishing boats arriving and departing. It starts to rain. How are you going to use an IPAD in those circumstances? While I'm sure it can be done (of course it can be done with paper charts alone), I would be much more comfortable with a dedicated plotter mounted at the helm.