Ductwork recommendations

Hi, looking for recs for HVAC companies that do ductwork. I have a single vent that's not blowing out air (the rest of the house has great, strong AC and we redirect air from rooms that don't get as much daily use). It's in our living room, which we use frequently and it's been consistently like 85 degrees in there 🔥 It's an extended part of the house, so there's likely some issue with the way the ductwork is installed. We just bought this house 6 months ago and don't want to pay to get a mini split - we want to see what else can be done more affordably.

Rincon air doesn't do ductwork but said they would give us recommendations to improve airflow, but they never actually followed up. Comfort zone was a no show. And I scheduled something with Samson & sons, but it's $100 for diagnostics and I was wondering if there are other cheaper companies?

Thanks!