has anyone had problems with leaking coolant from the heater core top hose going into the firewall?
Your vehicle is 6 years old so things break , fail , wear out and they have to be fixed so it really does not matter if anyone else had that problem because it is on your dime to fix.
just wanted to know how much the cost would be if someone had the same problem.
Problem is several variables. Is it the hose that is leaking? If so, is it conventional heater hose or a molded hose? If conventional heater hose with a clamp you could do it yourself for less than $5.00. Molded hose more dollars.
If it is the heater core itself then much more. The core itself is in the $100 price range, then labor to install.
Only an automotive repair facility can answer your question.
How often is the coolant supposed to be changed? Your car may be overdue or close to due for this anyway.
They’ll have to drain some or all the fluid out. Then add the cost of the hose and the labor to remove the old and install the new, refill coolant, run engine to get air pockets out of the cooling system, etc.
I’d guesstimate between $100-150. As Purebred pointed out, there are many variables, and this could well be an easy and inexpensive DIY project.