Interesting
If it's important, it might be worth checking that you can use SD card higher than 2GB.
AFAIK, there was a restriction that limited SD projects to 2GB because of MS restricting of FAT32, and SD licensing. (I was recently told that is no longer a problem, but I couldn't find any evidence)
'Arduino' - $15
GPS $35
box $20
SD socket $ 4
display $ 6
Misc $10 - buttons battery buzzer
SD $10
fudge $10 Contingency
Total = $110
If you can keep the PCB small, it might be pretty cheap to make one off from, e.g. from Sparkfun.