You found a beautiful original watercolor painting at a bargain price of $100 and can't wait to display it on your wall only to find out the picture frame will cost 2 times the amount of the artwork. This is a common issue but resolvable with a few hacks.
1- Fit it into a standard size frame
The most economical frames will be the standard sizes, 5x7, 8x10, 10x14, 16x20, 20x24, and 24x30. It may be possible to cut down the picture to fit within the standard frame size.
2- Buy a custom mat
If your picture won't fit into standard size frame, you can buy a custom sized mat to adjust your artwork size up to the next frame size but be sure to have at least 2" mat on each sisde as a border. For example, if your artwork is 15x18, the closest size standard frame is 16x20 but that wouldn't give you the minimum 2". So the next size up is 20x24, so you would want an exterior mat dimension of 20x24 with the inside hole cut out to be 15x18* giving you a 2.5" border on two sides and a 3" border on the other two sides. Depending on the dimensions of your artwork, this might not be an option if the two sides borders are too different.
* the opening should actually be 1/2" smaller than the actual picture to provide a lip the edges can hide behind
3- Buy a custom cut to size frame
If neither of the solutions above are an option, you will need to buy a custom sized frame. Some of the most affordable are frameless acrylic stand off frames that offer a touch of modern elegance.
Ion Acrylics offers custom sized frames for any size art work.