Do you need a license plate?
If not, any of the various playbikes will be awesome for you. Low maintenance, forgiving for a new rider, low seat height, soft suspension, e-start on most of them, cheap, etc. Specific recs:
Hondas:
XR-200 - available used for very little money and a great first dirt bike
XR-250 (might be a little tall for a first bike for someone your size)
CRF-150
CRF-230 (might be a little tall for a first bike for someone your size)
Yamaha
TTR-125L You might outgrow this quickly
TTR-230 Widely considered inferior to the CRF-230, but as a new rider, you will never notice the difference. If you find one for cheap, it will be fine. Note warning earlier about seat height - at your height and on a first bike, make sure you are realistic with yourself about how far away you are comfortable with the ground being
XT225 (07 and earlier) or XT250 (current model - more expensive) - If you need a plate, this is a great choice as a first bike.
Kawasaki
KDXD200 or 220 if you find a used one cheap and you are comfortable with the height
KLX 250 - if you need a plate and you are comfortable with the height
KLX 140L - this is its first year, so neither I nor anyone else has any experience with it, but its marketing materials show it as targeted to folks like you
Oh, and while I have no experience with them, I will parrot the opinion of others that the cheap China bikes are not worth it unless you are very mechanical and enjoy tinkering. Parts availability has been an issue for some who have bought them.