If you consider the core of the sun to be its center (actually, it isn't; but we'll handle that later), the speed of light would be determined by the distance it travels divided by the length of time:
696,000 km / 50,000 years = 13.92 km/yr.
To compare this to the speed of light in a vacuum, we need to convert the above into m/s.
There are 1000 m in a km and approximately 31,500,000 seconds in a year.
---> 13.92 km/yr x (1000 m/1 km) x (1 yr/31,500,000 sec) = 0.00044 m/s
This is very slow as compared to the speed in a vacuum because of the density of the sun. (Picture light as being a particle; it's being bounced around, therefore, it takes a long time to escape.)
Actually, the core of the sun is about 1/5th to 1/4th of the sun. Since light is not travelling from the center of the sun, the speed of light is still slower; reduce the speed by 1/5th or 1/4th.