Hi Sudeep, a colleague recently bough the Garmin Montana. It is not specially affordable but is a very good GPS. Garmin Oregon is similar to Garmin Montana.

I am familiar with the Garmin 60Csx and 62Csx, it is a resistant equipment to work in humid climates. I agree with Bonifacio, it is not so expensive and easy to operate.

I use Garmin Dakota 20: light, cheap and it's possible to upload personal cartography.

I usually work with Garmin 60Csx and 62Csx, like Galo. But now there is a new option Garmin GPSmap 64st . All of them are relativily cheap, weight is ok, and the new one has a very good improved signal (GPS+GLONASS). 

Please keep in mind accuracy issues. We've performed several studies in forested conditions....http://warnell.forestry.uga.edu/Warnell/Bettinger/GPS/index.html

In addition to the above answers, the Trimble TDC 150 GPS is very good for ecological work. This is because it has the capacity to take readings under tree canopy cover.

https://geospatial.trimble.com/products-and-solutions/tdc100