If it's a brand new site with a limited budget, six months is not enough time to rank well for searches that are seriously competitive.
Tread carefully here; few things are less fun than dealing with a client who has unrealistic expectations.
Even if you could, ranking for a handful of trophy terms is not the wisest goal to set nor the best way to define SEO success.
If you do things right the site would (eventually) gain traffic from the target terms, but it would also gain traffic from searches that you never thought of. It makes a lot more sense to measure SEO progress based on overall growth in organic search traffic, rather than just what the rankings might be for specific search terms.
It makes even more sense to define progress by tracking what new business results from the new traffic. That is the end goal, after all.