Trying to to temporarily fill it will not resolve the problem.
The longer you leave it, the worse it will get, and the treatment you will need can potentially be more expensive. Dental treatment is least expensive when the problem is minor. Major treatment requires more time and expertise and therfore will cost more. Dental insurance
does not necessarily cover all of the costs of dental care
, so there will still be an out of pocket expense.
Seek out a community dental clinic in your area that may be able to treat you at a reduced cost. If you can feel the cavity with your tongue, it is already moderate in size.