A restaurant website can cost anywhere from $0 a month on a free POS-bundled plan to $15,000 or more for a custom build with direct ordering. The published ranges overlap and disagree, because nearly every one comes from an agency or software vendor pricing its own service. No independent survey of what restaurants actually pay was found, so treat each range below as a seller's quote, not a market average.
Read the figures in three layers. First is the build: a one-time project fee from a freelancer or agency, or nothing if you use a builder. Second is the recurring cost: hosting, domain, maintenance, or a monthly platform subscription. Third is per-order and payment-processing fees, which can end up larger than the subscription if you take a lot of online orders. Owner.com's Flexible plan, for example, is $249/mo plus a 5% restaurant fee per order. At $10,000 a month in online orders, that is $500 in fees on top of the subscription. That is arithmetic on the published rate, not a vendor example.
Each row in the table names its source. Dates show when a page was seen or published, and a few vendor pages could not be read directly, so those figures are marked as secondary. Confirm current pricing with the vendor before you commit.