It might be difficult to find a Bosch drivetrain for less than 2k. And it will definitely not have a throttle.
To keep costs minimal, stay with the less powerful line of Bosch.
The Gen 4 CX will cost you. If you don't have steep hills or carrying a heavy load, go with the active line and a 500wh battery, you may find a bargain.
You will also want the widest tires possible- 2.6", not only for better traction on soft surfaces, but they handle the extra weight and use lower air pressure