"I am planning on buying edibles and wanted to know if it would be more logical and less expensive to just buy the cannabis oil and apply it my food during snacks/meals"
I actually do this for my own edibles! It is kind of a creepy way to buy cannabis, but you can buy the oils in syringes (i guess their technically applicators... anyways I wish they would do it in a way that wasn't so creepy looking). You will want to double check that the oils have been decarboxylated as well. That way they are active when you ingest them.
If we do some quick math: I can find in a popular dispensary in SF, that a cannabis cookie of 120mg THC is $12. You can buy a gram applicator that is 70% THC for $40. That works out to 700mg for $40. We can already see the cost savings :)
You can also get a bit scientific with this and try to use edibles that are fatty to increase the bioavailability of your oil.
Buying concentrates intended to be vaped or smoked will not work if they have not been properly decarb'ed, so you cannot just grab any hash oil unless you plan on decarboxylating the oil yourself. Care by Design makes a great 4-1 CBD:THC. I had a lot of success just dropping a dab of oil into a sandwich.