Hi,

Either you can set the default quotation validity to the quotations from the sale settings or you can add some custom codes or modules to over come this.

There is module from OCA which enables the recalculation of the price and description of the product in the sale order lines, please have a look at this module: Price recalculation in sales orders

Using this module user has to click the button to update the price, you can try to automate the button click from the code using the automated action while updating the product price or by over riding the write method of the product model.

Thanks

This is tricky requirement, although not unusual.

Let me suggest best possible solution, depending on your business needs, you can proceed with.

Auto-Cancelling Quotation (or any custom-state): 

Run a Scheduler: Check for quotations which are lying for longer period, & set it Cancel Stage.

In front-end, ie for Customer, suppose if For any cancelled Qtn, when Customer wishes to convert into Order, that time, let System check the prices for any price-change, when found let it alert the Customer, informing the same & proceed with New Price -- during which system will update price & proceed with Confirming Order

Note: This Can also done, without using scheduler, ie when there is any change in price of that product -- u can perform the same by introducing flag or state into its associated Qtn