Can a Ethernet USB Dongle be instead of Ethernet shield for arduino in order to cut costs?
No, not directly. As @Majenko pointed out its possible but most likely over your head. I am not a big fan of the ethernet shield as I like to use my Arduino for prototyping and then build the project with the components. There are a 2 easy alternatives which are inexpensive options for accessing a network or internet via the Arduino
- ENC28J60 Ethernet LAN Network Module
- Esp8266 Serial Wifi Wireless Transceiver
Both are inexpensive (between $5 and $7 USD). There are tons of tutorials on line to get you up and running
Possibly with an Arduino Due in USB OTG mode if you want to spend months and months (or even years) delving into the USB specs, reverse engineering the driver for the USB dongle and writing the software to get it working.
"Possible" but certainly not worth it when you can use a simple Ethernet shield and have it all working within a day.
And definitely not possible on anything like an Uno, etc.
Also it's possible on an Arduino that runs a full operating system (Linux) like the Edison or (possibly) the Yun (OpenWRT side of the operations, not the Arduino side).