I have no idea what these cost but a complete car plus engine mods wont be cheap
https://www.rotax.com/en/products/rotax-powertrains/details/rotax-1630-ace.html

Or totally off the wall with the super clean 160bhp 850 eTech
Power is made at 8000rpm so probably need some engineering to suit the Panda gear ratios (1.4 litre 100HP makes it's power at 6000rpm)
https://www.rotax.com/en/products/rotax-powertrains/details/rotax-850-e-tec.html

The Rotax two strokes are a long way from the smokey things of the past. They are cleaner than competing 4 strokes and offer similar mpg figures.