Certainly. Particularly if it's run by a two stroke engine. Modern engines covered under CAA regulation have combustion efficiencies well in excess of 95% where as a typical two stroke engine runs at around 65% combustion efficiency. You're 300 hours number is a lowball number that would be appropriate for a urban home owner in Chicago but not a suburban home owner in Charlotte who will have both larger yards and longer seasons so a 400 to 600 hours would be more accurate. But for the sake of argument lets use your 300 hours figure and assume that represents 1/2 gallon of fuel at todays price of around $2.50/gal. With a 30% inefficiency you can account for an initial cost of around $175. In addition these small engines represent about 25% of total emissions in urban areas for VOC's (volatile organic compounds aka hydrocarbons) NOx (responsible for ground level ozone and acid rain), carbon monoxide (a green house gas and a respiratory toxin) so your talking about a substantial reduction in the cost related to these pollutants which impact quality of life, health, agriculture, etc. Now that's just for small two stroke lawn mowers and weed wakers. The cost benefit for motor scooters and motorcycles would certainly be saved in fuel efficiencies alone.
In addition the $300 cost quoted is for retrofitting two stroke engines in small motorcycles which is arguably a difficult sell, particularly in places like SE Asia, where a working person might only be making a few hundred dollars a month but again is a cost that can be justified by increased fuel efficiencies. At the front end manufacturing of two stroke engines with direct injection is only around $5 to $7 per engine which, obviously, is easily compensated for by increased fuel efficiencies.
In the USA it's a moot point as regulation has been put in place by EPA where OEM's of small engines will be required to manufacture them with direct inject technology phasing in through 2011 and 2012 and required there after.