on the hubsan 501s side... 20 min flight time and $200 ready to fly (controller, battery, charger, fpv screen etc) with a built in FPV camera AND gps... is hard to beat... the gps makes it super easy to fly... I an put it up, put the controls down, and walk away... when the battery gets low it'll even land itself.. but it does have a few other modes including full manual and elevation hold mode.
also has a neat return to home feature... flick the switch and back it'll come and land within inches of where you took it off from... which is neat.
on the phantom side... if you are going for a quality filming rig for a reasonable price I don't think you can recreate this quality AND flight time mix for a similar price... it's easy (at least around me) to find used a phantom 3 or higher with 4k camera, extra battery, and some with a backpack "case" and tablet for $500 or less...
that being said... I like building things so the building idea does interest me... I'd love to start with something like this
https://www.ebay.com/itm/S500-500-Q...e=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649
you can also find down to 450mm and up to 630mm or so...
on a side note... looking around I couldn't not mention this guy...
https://hobbyking.com/en_us/hercule...JSYQZ-JKIu-hX1hk5ZEaAhSHEALw_wcB&gclsrc=aw.ds