Most are very reasonable, especially when you compare their fee to the costs of paying others for estate and tax planning advice, for investment management, for preparing tax returns, and for investment trading commissions.
A corporate trustee typically provides all these services and more for only a small percentage of the value of the assets they manage for you. (Fees are published, so you can find out what they are.) And because their compensation is based on how much those assets are worth (instead of on how many trades they make for you), a corporate trustee is motivated to help your assets grow.