I would love to fix up this ancient trumpet...? Yesterday I found a trumpet at an antique shop for five dollars....

Yesterday I found a trumpet at an antique shop for five dollars. It is slightly dented all over and requirements to be polished. It only have one valve moved out: the one closest to the mouthpiece. I actually enjoy the mouthpiece and can buzz it and make a nouns, like one and only four pitches, out of the whole trumpet. What do you deduce is the cheapest way to fix it up? Thank you.
What is the average cost to fix a...
Answers:    If u r handy, rummage through the Bay for parts. Taking it to a music store will cost u more than buying a good used one.
It might be an antique. Research the brand since you make any modifications. Might be worth more as-is!
If none of the above are nifty ( not handy, no parts on eBay, not worth anything) just use it as a display item over the door or mantle.