You could go to AutoZone and spend hundreds on "cheap upgrades". I would suggest getting your truck and really digging into it, find out what you like about it and what you would want to change. Ideas will start to come to you.
Then start pricing out those ideas and start from the bottom. Sometimes 1 quality upgrade is worth 20 "cheap" upgrades and totally worth it.
To throw you a bone though, a cheap upgrade that looks great and is useful is converting your reverse, license place and bed lights to LEDs. Looks great, helps when reversing.