How can I make a budget like this in a spreadsheet? I have the budget, total money spent and money left part put in, but I can't get it to automatically subtract when I put the numbers in.

\begin{tabular}{l|r|} \hline Budget: & $1,000.00 \\ \hline Total Money Spent: & $904.78 \\ \hline Money Left: & $95.22 \\ \hline \end{tabular}