I own an older Innova I bought from Amazon. Even Walmart has them hanging on a blisterpack rack IIRC.
you also have the option of a cable/laptop/software combo, a bluetooth/laptop or smartphone.
Years ago, I read of folks with cheap harbor Freight units and ebay units that would not read the ISO protocol that Subaru uses but if you stay with a known or well reviewed brand/model - you should be OK. Buy a newer Innova if you think you will be using the unit on friends/relative cars that might be CAN bus. Or make sure the unit you buy can be flashed/upgraded.
you can spend from about $20-25 up to hundreds I guess. Might find someone selling one used that has upgraded. Personally, working with a handheld unit with a cable is fine, cable plus laptop is kinda a hassle and not the best to loan to a buddy or haul to a remote location in bad weather.
Mine has been used on other people's cars more than my own, but I'm still glad I bought it. I think it cost $99 several years ago.