The two main pieces of the cost
The Estate Administration Tax is the government charge tied directly to the value of the estate being probated — the larger the estate, the more tax is owed, though the exact rate structure is something to confirm directly with a lawyer, accountant, or the Ontario government's current published rates rather than relying on a general estimate here.
On top of that tax, most estates involve legal fees for preparing and filing the probate application, which vary depending on how complicated the estate is — a simple estate with one property and clear beneficiaries costs far less to administer than one with multiple properties, disputes, or unclear documentation.
What makes probate more or less expensive in practice
The biggest cost drivers are usually estate value (which sets the tax), how organized the deceased's records and assets were, whether there's more than one property or business interest involved, and whether any beneficiary disputes the will or the trustee's actions. A well-organized estate with a clear, uncontested will is generally the fastest and cheapest to probate.
Some smaller or simpler estates may not need full probate at all, depending on the assets involved and how they're held — worth raising directly with an estates lawyer before assuming the full process applies.