Is there any way to emulate perfectly a OnePlus device?

Short answer: No. You can not run a Cyanogen OS device on the Android Studio emulators. However, there is a workaround where you can make a oneplus one clone that works on android:

• Click on the “Run ‘app’” button
• In the dialog, click the button in the bottom left corner with the text “Create New Virtual Device”
• Click the button with the text “New Hardware Profile” in the bottom left corner
• Enter the specifications and the name (Some examples: OnePlus 1 specifications, OnePlus 2 specifications, and OnePlus 3 specifications)
• Click Finish
• Click Next
• Choose the system image (It will show a dialog, if doesn’t then skip this step)
• Click Next
• Choose your preferences
• Click Finish

Hope It Helps! Good Luck!

There's no way to perfectly emulate any phone. Running Nexus 5 emulator would bring you a 'device' with some proper values like screen coordinates or Android system version, but it won't make you sure that if it works on an emulator of Nexus 5, it would work also on the real device.

As I know, OnePlus is using Cyanogen OS (so it's not the same as you would find on Nexuses or Samsung devices), so one opportunity is to find a cheaper option phone with this custom Android system like Willey Fox brand devices.

Also, check your app on Genymotion emulator - it also uses a custom Android system based on CyanogenMod, but as you already know, the best way is to check it on a real device.

Hope it will help