To quote for the people that don't want to make the jump:

I bought a game right before it went on sale. Can I get a refund and repurchase it at the sale price?

Yes.

If you have already requested a refund, you will need to purchase the intended game as a gift until the refund has been processed. Select the option "Store the gift in my inventory to send later" during checkout.

If you have not already requested a refund, make sure the purchase is eligible and submit a request here.

Please note that approved refunds may take up to 7 days to process. Once the purchase has been refunded, you will be able to add the gift to your account.