As with any firearm, it is not possible to accurately appraise a gun without seeing it. Recommend that you see a local gun dealer for an appraisal.
You can also do your own investigation by looking at other models being sold that are in the same condition as yours. Try the gunbroker.com or a periodical called "The Gun List"
You can also reference the Blue Book of Gun Values which can be purchased on line at various retailers.
Also reference the Standard Catalog of Firearms. Each will vary but the value is probably the average of the two.
100% mint condition book values range from $325.00 to $450.00.
Need a detailed description
100-500 USD
The U74 suffix to your serial number indicates that your Browning challenger was made in the year 1974.This also revels that you have a Challenger I because the Browning challenger II was not made until 1975.You should have Plastic wraparound grips which were only made on the challenger I in 1974.The challenger I was produced from 1962-1974.The challenger II was made from 1975-1982.I hope this helps?
The Deputy - 1959 The Challenger 2-22 was released on: USA: 25 February 1961
Browning.com has a sn function under customer service.
500-700 or so
Basically impossible to value with your description.
500 USD
Challenger
2-20 usd
0-375 usd
The 2 letters PX in your serial number indicate that your .22cal browning BL was made in the year 1983.