Yes both the 11-48 and the sportsman 11-48 are the same gun. The only difference is the sportsman came standard with a plug to limit capacity to 2+1 to comply with hunting laws.
Don't know for sure which you mean... Sportsman 1930-1947 Sportsman 48 1948-1968 Sportsman 58 1956-1963
3
http://stevespages.com/page7b.htm
100-200 USD
First of all you have the "sportsman 48", "sportsman 58" and the "sportsman". If it is a plain sportsman it's value depending on it's condition is from 150 to 200 dollars.
50-200 or so
50-135 US Dollars
Check the date stamp on the barrel. The table look and details are on the manufactured date link of the Remington Society of America.
Should be on the action, Sportsman could be the 48 or 58 semi auto. Sportsman models have little parts left so try not to break any.
Date code stamped on left side of barrel, go to Remington Society of America for diagram and chart.
If you look closely, I think it's a Sportsman 48 instead. Anywhere from $100-$300 depending on condition and options.