Sounds like a good price if they know what they are doing.
It's certainly not easier to do it yourself,. Never looked at the Ion myself but your going to have to learn how it all works, programmes and goes together.
For example, you say hooking it up to the inet will be the easy bit, but do you know where to enter the IP settings on the panel?
It depends how much you value your time versus your money, if you do DIY it maybe best to read the manual a few times and then get the panel sensors enrolled and tested first.
If you have any further specific questions break them down in another thread, you may find someone that has used the Ion can point you in the right direction.