We get asked this every now and then. Obviously, if you have a $700 air assist gun, it pays to throw new seals in it. If an inexpensive airless gun costs $128, it may not be worth it because a new OEM kit costs $75. Take into consideration that a new gun comes with new tip and guard and that makes it pointless to even repair it yourself. Consider aftermarket repair kits at $40 and save up a small bucket of guns to make it worth it. If you have just 5 guns, you can save $175 over buying new guns, even if you take the new tip & guard into account.
So, it doesn't really pay to repack one inexpensive airless gun. Don't throw it out though because once you get 4 or 5 guns saved up, it certainly repays to fix them up. It will also pay dividends to have plenty of good guns in stock, ready to go. Consider also buying the same model gun all the time and it will be easier to stock filters and kits for an even slicker operation.