I can see the usefulness of this when wanting to see the total quantity for a given card, e.g. you want to see which cards you own more than 2 playsets of (regardless of edition) so that you can get rid of the rest. In such a scenario, it would be useful to sort by the Count column but with other qualities ignored. In the ideal version, you'd be able to choose which qualities to ignore and which not. For instance, you might not want to include foils in that count, since you deal with them separately. Same goes for language. Or, you may not care one bit about any of those things, and you want to combine cards no matter their edition, condition, language, and foiling.
I don't see how useful it is with something like price, since price can often be very dependent on which edition a card is from (things like it being an old, low-print-run set or a unique art for that card can drastically increase the price of a card; for example, the Guildpact art of Godless Shrine costs twice as much as its Gatecrash and Allegiance variants, while a $3 Underworld Dreams costs $80 when it's from Legends). Even if cards WERE collapsed and sorted by price, which price would it default to using -- the high or low price?
In any case, the following guide is how you can achieve it manually.
Export your inventory to CSV.
Make a copy of that file as a backup; store it somewhere safe.
Open the other copy of that CSV in Excel.
Delete any columns that you don't care about.
Save and exit.
Back on Deckbox, in your Inventory go to Tools > Remove Everything. (Don't worry; we have the backup from earlier!)
Go to Add Cards > From a CSV File and import the file you edited above.
Play around with it to your heart's content!
When you're done, Remove Everything again and re-import from the original backup. Done!
If you do this type of filtering often, but don't add/delete cards from your inventory often, then I recommend keeping the edited CSV file around for later use. In fact, you could make multiple versions of it — one that ignores foiling, one that keeps it distinct, one that ignores language, one distinct, and so on — based on your specific needs.