Application fee is only $100 in Canada.. but you have to pay yearly maintenance fees to keep the concept active.. miss the payment and your patent is void and not revivable.
A patent agent or lawyer is going to add, at minimum $4000 to the equation... more than likely $7500.
Defending the patent if some big corp decides to copy it anyhow... out of most peoples price range... and I'm speaking for experience there. I own all the patents for Enviroseal electrical boxes (plastic box, foam seals for wire push thru and snap over vapour barrier wall board sealing ring). Thomas and Betts copied them and flooded the market with their product, already having ins with CTC / HH / HD / Ideal / Westburne etc, and not much we could do to defend it.
Trying the royalty idea is a gamble ,, big gamble,, that requires some real finese to not get taken for the idea. As HG points out... a real good spot to send your idea to yourself registered mail and never open it... in fact send it Registered mail to your lawyer as well and instruct them to do the same.