That really depends on what kind of resources you have at your disposal and your own abilities. There are quite a few upgrades that can be done for almost nothing if you already own the tools. Just don't fall for gimmicky "upgrades" that just lighten your wallet.
Setting a proper squish gap never hurts and can be done for relatively cheap with a glass table top and some sand paper. You need a pair of vernier calipers to measure the gap and your progress though. Good cheap pairs cost around 30 to 40 bucks. A cheaper pair can suffice if you aren't trying to aim for micron levels of tightness.
Cleaning up ports in the cases and jug is "free" power. Not actual port timing work, just gasket matching and smoothing things out. Need a rotary tool and some burrs and stones though.
They do sell a "Phantom Style" exhaust for your engine that uses the larger diameter pipe and muffler as the Phantom. It's 30 bucks (last I looked at least) and will offer a benefit of increased flow without all the noise. That being said you can also spend the same money on a mz clone pipe and see a better power increase. The downside is it will be very loud if you also don't put a muffler on it of some sort.
Free would be the extra hole some drill nto the muffler cap, but this does again come with a small noise penalty.
Really its not great for a 2 stroke to have that no baffle because you may as well be just running header, no back pressure, your motor will not last a while like that.
Really its not great for a 2 stroke to have that no baffle because you may as well be just running header, no back pressure, your motor will not last a while like that.