Without a PC for keeping the database up to date on a 436HP (or other database scanners), 'scanning by zip code' might not be very effective.
With the 436HP, the NXDN channels listed for the are in the database. So, as long as the database is at least current when the scanner is acquired, he would be able to use the main database, along with a location & range. But, if there are changes or additions to what systems & channels are used, those would not be loaded unless the database can be updated, or the changes entered manually..
Yes, you can program a 325P2 through the keypad, but that is tedious, especially if you are also including the text tags. For that matter, a 436HP can also be programmed manually if you were to start out using the database then use the keypad for any additions. But it is much faster, easier, and more accurate if a PC is used. The software for the 436HP, Sentinel, is not a resource hog. You don't need a blazing fast processor and a lot of memory. If you look around, you can find a previously owned PC or laptop in the $100 to $200 range; it would need to be able to access the internet. To use your Mac, you'd need Boot Camp, Parallels, or something similar, plus a copy of Windows. If you don't already have those, the cost of purchasing & installing them is likely to be near the cost of just a used PC.