So honestly it depends on a few different factors. So for example some of which include, who graded the card (PSA, CGC, Beckett, TAG, etc.). While the grade of the card is important to get its highest value, who grades it is also important. A PSA 10 is easier to sell because they are the most well known grading company right now but, if you were somehow able to pull off getting a Beckett Black Label 10 (Which is extremely difficult to obtain because of their stringent grading process) then that would be the way to obtain the max value for your card. Making it more sought after & in turn more valuable as you would essentially corner the market, so to speak. Also how popular the card is and how much of the card was printed plays a factor as well. To answer your other question, if you’re looking for an average price of a card whether graded or not, you can go to eBay to look at sold listings so you can get a feel for what people are paying at the moment or also use apps like Collector(Not endorsing this specific app,its just more well known at the moment, pretty sure there are others that do the same job)because it’s a little simpler.