This is a low cost way to install a pull-up bar in a standard doorframe. This will put holes in the wood, so you have to be okay with the permanent installation or a bit of patchwork when you want to remove it.
I bought all the materials for this project for $17.13.
What you'll need:
1 iron pipe 3/4" (cut 1/2 inch shorter than doorway)
4 corner braces 3 inch
4 nylon spacers 1/4 inch by 1/2 inch
4 #10 washers
4 #10-32 3/4" machine screws
4 #10 nuts
8 taper head screws 3 inch
Adjustable wrench, or 3/8 inch open end wrench
Two tapping blocks
Drill w 5/32 bit
Step 1: Build T- Bracket
Attach two L-brackets together as shown. I use the oval head screw directly through the first brace, then the spacer, then through the second brace, followed by a washer and nut.
Do not fully tighten the screws yet, since the movement will make it easier to insert the assembly into the pipe. The .26" inner diameter of the nylon allows some play, so you will want to get it square before the final tightening