How to use a condition on data validation

Hi everyone,

I have attached a file that has my problem in a simple form.

I would like the drop down list in D15 to show only the house price values which are equal to or lower than that of the budget.

The budget currently shows 50 (cell A2) so i would like the drop down list to show 20 and 50 (eventually i will link it to the names to show the names rather than the budget. )

If i change the budget to 49 only the 20 should be in the list etc.

hope this is clear

thanks