$50 to over $1000. You didn't give any specifics to help narrow it down. All we know is that it's a rifle in .303 British service... presumably, it's probably going to be a Short Magazine Lee Enfield, but we don't know the specific model, what country it was manufactured in (SMLEs were manufactured in many countries), or even if it is an SMLE.. it could be a Lee-Metford, it could be an Enfield Pattern 14 rifle, for all we know, it could even be a Canadian-made Ross rifle.
number5 mark 1 enfield 303 british jungle carbine
50-500 USD depending on EXACTLY what you have, condition, accessories, etc..
See the link below to a good Wikipedia article on the Lee Enfield. There are several DIFFERENT .303 Enfield rifles.
http://www.diggerhistory.info/pages-weapons/303.htm
The .303 British and .303 Savage are not the same. Only purchase the caliber that is printed on the barrel.
Value of NAY firearm is based on exact make, model, and condition. If your Enfield is in the original military configuration (not sporterized) and in good condition, value could range from about $250-$400.
The standard issue weapons were... Webley revolver in .455 Webley Short Magazine Lee Enfield No. 1 Mk III in 7.7x56R (.303 British) Enfield P'14 in 7.7x56R (.303 British) Vickers machine gun in 7.7x56R (.303 British)
The cartridge is sometimes called the .303 Enfield or .303 British (or even 7.7×56mmR). Do not attempt to use other ammunition.
I bought mine for $228 Canadian
50-250
125 USD
125 USD