For typical PPL flights I think the maximum anyone is likely to want to pay for is a package of
1 - Your route determined
2 - Plog Created (reflecting forecast winds on the route)
3 - Flight Plan filed and managed for you (notified to the correct agencies if you are VFR or mixed VFR/IFR)
4 - A sensible weather briefing pack
5 - A chart printout
6 - Plates for your departure, destination and alternate
7 - A file you can upload to your GPS
8 - A Gen Dec created for you to carry send
9 - Updates on slot times and ATC messages (like , hay you don't have a PPR number so you are not going to get landing clearance - applies to light jets more than spam cans)
Getting people to spring more than a 10er for that list is going to be hard. Also, there are a number of existing operators already providing most/all of the list.
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You then move on to the things that are more costly to provide and much less relevant to the PPL
1 - Selecting which handling agent to use and booking it.
2 - Booking catering, limos, hotels, at the destination
3 - Arranging overflight permits
4 - Arranging fuel deployment (for remote locations are Avgas burners )
These are all highly manual processes that are provided by specialist support agencies (and Ops Departments)
On hiring a GPS... I am struggling to picture someone who can afford to fly IFR and can't spring a couple hundred quid for a quite good gps (or less than 100 for 'last years model' used).