But customs like to charge a fee for items over a certain $$$ amount
The threshold is about $30. You can actually get away with it up to about $60-$75 some of the times on mailed in items, and almost never on anything over $100.
Why they assign that handling fee is usually (their excuse) to cover inspection of the item and checking to see if it can be cleared.
The ironic thing is that, if you cross the border IN PERSON you do not get assigned this fee for these amounts, and yet a item imported via the mails merits it.

I've had charges that were higher or lower myself too, so I'm equally confused as to just what formula they use, and the Canada Customs info on this is vague.
The one thing you do want to avoid is using any kind of courier or express service to ship stuff up, because they WILL use a customs broker. The Customs broker basically does the same thing that Canada Customs already does with the "handling fee"--they "guarantee" the good can cross the border. In doing so they become a kind of redundant middleman with their hand out--BUT, if you agree to use a courier service to ship the goods into Canada you are also agreeing to the use of a third party customs broker--read the fine print.
What sucks is these jokers can add another 25% on top of what you have already spent ( item and shipping)
I just avoid any retailer or transaction where the sole shipping option is a UPS, FED EX or other courier services. Good ol' USPS doesn't use a customs broker for items sent via surface or airmail.
Its probably a good idea to read through the Canada Customs pages on-line that cover importation of stuff like this, just to get a better idea of how it works.