I have a winchester model 1890 22 long pump rifle pat. june 20,1888 - dec. 6 1892 serial number 783212 and was wondering what the value might be

The best way to determine the market is to search the Internet or E-bay for your rifle and see what prices are offered.

Here's a similar one
http://www.gunsamerica.com/903620142/Guns/Rifles/Winchester-Rifles-Pre-1899-Pump/1st_model_1890_22_long_caliber.htm
On yours, if it's in good condition, you won't get more than $2000.