Welcome back to the trumpet.
A fair price on a used horn is one that both buyer and seller are OK with.
In any case I suggest getting some good oil and slide grease.
I use Ultra-Pure;
Ultra-Pure Trumpet Valve Oil & 2 Lubes Great on Monette - eBay (item 150205249273 end time Jan-19-08 17:21:11 PST)
Renenber to be gentle with yourself, especially at first. Rest as much as you play and as soon as your chops get tired and your tone falls apart the stop for a longer rest.
For the first week or two you might only be able to play a few minutes at a time but it does come back.
Have Fun!