Can I pay monthly for a Apple Watch

There are some options for some products in the Apple Online Store, check the terms for your country and the options for credit. Payment, Financing, Refunds and VAT - Shopping Help - Apple

Hello,

With apple i think you can finance a apple watch, but i highly advise you not too as it may be expensive in the future with interest

If you want the cellular version check whether your network will bundle it into your service contract.