A better choice in harnessed seats for those on a very tight budget would be the Cosco Scenera or Evenflo Tribute (Convertibles to get kids to at least about age 2 or 30 pounds rearfacing, then to about age 4 forward facing), or the Evenflo Chase for kids older than age 2-3 who are forward facing. This one becomes a booster later, but I can't recommend it as that, it has the same problem as the Cosco seat that it causes the belt to ride up on the belly. But if you just use any of these seats harnessed, they aren't unsafe. The Chase has top harness slots about 2 inches taller than the Cosco and could last about 2 years longer, heightwise, as long as the kiddo is average weight (top harness limits on all these seats is 40 pounds). A slightly more expensive choice is the Evenflo Generations 65, which has a higher harness weight limit at 65 pounds, and taller slots, like the Chase, about 16.5 inches (compared to about 14.5 for the Cosco seat you have now).
Here's what we mean by 'doesn't work well as a booster'... (blog review with pictures)
http://carseatblog.com/?p=1331 And despite the hip portion now being cut out lower, it still does not allow the lapbelt to ride lower on the lap.