Hi All:) This is my first post here...

I'm a student and my summer project involves taking a lot of GEO tagged photos - I have a good budget for it, so i need to find the optimal solution to do it. Basically, i'm going to map some plants and rocks positioned every 1-4 meters from each other.
Every day i'm going to make 1000 photos and i need them to be geotagged with the highest possible accuracy. So I looked at several options, but would really appreciate your expertise.
PRESS of ONE BUTTON (no post processing)
Option 1: built in gps cameras
try 1: Lumix TZ 20 with built in gps
The problem here was that the camera is for tourists so the GPS is slow to update (every N minutes).
To get the current lock one needs to wait 1-3 minutes which means that i need to relock and wait 1-3 minutes after i move to a new position (plant/rock).
try 2: reading on this site i found that Sony has a camera with built in gps and it has the same problem
Option 2: External GPS attached by cable
Try 1: Nikon d3100
Nikon cameras have special GPS slot t connect new Nikon gps device - which costs almost as much as the camera

some 3rd part gps are available, but i don't know the accuracy. (advice appreciated)
Garmin eTrex H could be attached too - and my intuition hints that this would give me the best accuracy
Option 3: POST PROCESSING by using Garmin eTrex 10 (or similar) and software to geotag photos later
Garmin eTrx 10 standardly provides 10,000 geo tags/logs but i couldn't fine any information on how many logs are per track.
e.g. if i update the coordinates every 10 seconds in one hour i'll get 360 points and if per track it can only save 500 points it means that i have to do dome additional tricks every 1.5 hrs....
Do you have any info - whether Garmin etrex 10 could save more than 500 points (e.g. all 10k points) in one single track
so i can use it whole day (14 hrs)
Option 4: Open for your suggestions
thanks