I was once a baller on a uber-tight budget. I know what it's like to want to play but not have the gear or $$ to go. I have a cheap suggestion for barrel blockers. It will require a less-than $30 investment at the hardware store, but can net you about 30 to 35 blockers that work really well:
1.) Get some 1-1/4 in. PVC pipe or 1-1/2 inc. PVC pipe - Home Depot has 10-foot lengths for approx $4.50. Cost - $4.50 (The inside diameter of the pipe must be greater than 1 inch to go over most barrels)
2.) Get some cheap bungee cords at the dollar store - they can sometimes be found in packs of 3 or as many as packs of 6. You'll (ideally) only need 1 cord per barrel blocker. Cost - about $10.00 (in 3-pack, less for larger packs.)
3.) Get at least 3 of the following: 1-1/2" Schedule 40 Cap - Contractor Pack (qty 10 caps per bag), price: about $3.50/bag. Cost - about $10.50 for approx 30 caps
4.) Get some PVC glue. Go with the 8-oz size. "Oatey 8 fl oz LO-VAC PVC Cement -$4.44". Cost approx $4.50.
Steps to assemble:
1.) Cut the PVC into 4 inch lengths. This will convert the 10-foot pipe into about 30 smaller ones.
2.) Drill 2 holes on one end of the pipes. We will be threading the bungee through these later.
3.) Take the caps, and glue them onto the pipes opposite the end you drilled the holes into.
4.) Unwrap the bungee cords, and cut off the hooks. If the bungee's are the corded type (meaning they're actually more than one "cord" each, separate the cords. If the bungees are the rubber-band looking type, do not separate the strands.
5.) Carefully thread the bungee through the holes drilled through the PVC. You want to thread them so that the knots you make in the bungee end up on the outside of the pipe. This way, if they unravel, you can fix them easily, and you don't have anything interfering with actually using the blocker on a paintball gun's barrel.
Once the glue dries - you'll have about 30 barrel blockers that most fields will accept as "safe". If you wish to make them even more effective, spray paint them fluorescent colors so that they're easy to find if dropped. And since they cost about $.98 cents each to make, losing one or two won't impact your team's bottom line that much.