Pay per use keyword research tool instead of monthly subscription?

Hi everyone,

Does anyone know any keyword research tool that provide premium features on pay-per-use basis (i.e. search one time, pay for that), instead of a monthly basis?

I'm looking into the habit of doing keyword research for writing a few articles , but considering for the time being I'm using it about 1 or two times only per month, paying for a full months feel a tad wasteful.

I'd reconsider the monthly payment once I'm more financially stable or using it at more frequently (at least more than 15 searches per month).

Thanks for any suggestions!