bigolbug:
I have started working on the Transmitter circuit. You mentioned using a mosfet driver chip. what about a regular mosfet transistor (data sheet below)? The mosfet, i assume, will connect to a Tank circuit before feeding to the transducer?
No, driving the transducer using a single mosfet would be very inefficient. I suggest you a mosfet driver such as TC4420 or TC4429. Use an SMD adapter board if you find it difficult to solder. You don't need a tank circuit, the transducer behaves like one already. I would use a series capacitor and inductor between the mosfet driver and the transducer, tuned to 200KHz. Ths capacitor avoids putting DC across the transducer and the inductor suppresses the harmonics. Put a 10K resistor in parallel with the transducer for the capacitor to charge through.
As an easy alternative to the mosfet driver, you could drive the transducer direct from an Arduino pin through a 100 ohm series resistor and capacitor, but the transmitted signal will be lower. Using the mosfet driver, you can drive the transducer with a higher amplitude such as 12V p-p if you have a 12V supply available.
bigolbug:
What about using a VCO attached to an amplifier? I searched for VCO's and found some but they operated in frequencies above 200 kHz. If i went this direction, could i use a PLL and drive it with PWM voltages connected directly to the VCO?
What's the point? As I pointed out, you can get the frequencies you need from the mcu anyway, and they will be more stable than you would get from a VCO.
bigolbug:
I am considering a 1200 baud rate. I will have a total of 6336 bits to transmit and so considering transmitting at ruffly 6 bits per baud. Would this make sense? Hopefully this baud rate will not result in to much multipath interference
Using 1200 baud rate with 1 start and 1 stop bit, you will get 1200 * (8/10) bits per second, so it will take 6.6 seconds to transmit all the data. Have you considered whether you can represent the data using fewer bits?