Do you have a track nearby? If so, find out what classes they race. Slash spec racing is really popular, and it's perhaps the cheapest way to go racing. Your T3 would still be fine at the club racing level, and it's still a good truck to run on the track. Parts are also still easy to find for it. Electric has come a long way, brushless and lipo are a hard combo to beat. More power than nitro without the hassle.
ARCTIC DOG RACING (Nitro free since 2009)
"Straights are for fast cars, curves are for fast drivers...."
8ight-E / 8ight-TE / T4 / Slash