Buy instant oats and shake with whole milk 100g oats+50g whey. Eat some almond or other fruit rich in good fat. It's a very cheap method to bump your calorie intake
Enjoy

Look into mass gains by iforce nutrition. All the carbs in it come from oats and quinoa instead of sugar and shit and it's cheaper then any other product. Great stuff I been using it for a while now.

Use weight gainers as a last resort. I am not exactly sure what is in it but a lot the mass gainers just contain simple carbs as the calories which can wreak havoc on your insulin sensitivity and the only mass you will gain from it is fat and not the quality weight you are looking for. So if that is the case with the Dymatize I would look for something else.