Just want to ask if the wordpress themes is a one time payment when i buy?

Yes one time only to buy the theme. The support expires after six months but you only have to renew the support if you need support from the author.

Thank you FWdesign, link below is the one im talking about. The spectrum themes

This policy applies to all themes. You will get updates till the theme remains on the market. Support by default is for 6 months and can be extended to 12 months at the time of purchase.