Ardupilot can be used?

can i use ardupilot for my project . is it still supported?

yes you can. It is supported, and is probably the best open-source realtime autopilot.

i am doing a new project . would it be still supported?

I think the apm is already old for the new features of ardupilot and not fully supported. Better you look for new fc generations (x2.1 - x2.1-777 - pixracer r15 - pixhawk mini cube pink version - pixhawk cube orange version)

is there any device in the price range of arducopter with similar functionality?

New fc generations are more powerful…you must consider your project and future expansions you need.
You can check the regular pixhawk 1 but you must consider that the old silicon can be an issue coz 1mb instead of 2 mb.

Ardupilot/Arducopter is firmware. There are many Flight Controllers that are supported by Ardupilot. Some are quite inexpensive. The Omnibus F4 Nano for example is ~$30.

With 2 Mb this one:
Pixhawk clone 2 MB

MicroPix 2MB really economical:
MicroPix 2MB

for integrating with raspberry pi 3 model b+ under 40$ . for auto navigation using GSM module and hosting on cloud. please suggest

Better you choose the pixhawk… just look for the pixhawk who support the 2mb

If it has an available serial port and runs Ardupilot it will work. There are many to choose from. Ardupilot needs 1Mb to run which is what many of the boards in the link I posted have. A Matek F405-STD is ~$30. AIO versions of F4 and F7 boards are ~$50.