The Smart Parts Ion is a fantastic gun, in the sense it can be upgraded easily and it is not the most expensive gun. There are not nearly as many upgrades for the Piranha.
The Ion is considered higher end with a different bolt style, body, board, feedneck, and barrel. The Ion is also much better on air and faster. Though the aftermarket upgrades are very similar.
This bolt is an aftermarket accessory for most smart parts gun. This bolt lowers the operating pressure of the gun as well as helps the accuracy. The bolt fits any ion, vibe, SP-1, EOS, and Ion XE
There are a few places where someone could purchase a Smart Parts Ion paintball gun. A store like Sears, and websites such as trademygun, and ultimatepaintball, all sell Smart Parts Ion paintball guns.
A used Smart parts Ion can be sold for around 100-200 dollars depending on condition and what your willing to sell with it.
It depends on if you think you will stay with it. There is the Tippmann 98 Cutsom for woodsball. There are alot of things you can do with this gun. And by Smart Parts they have the Vibe and the Ion. The Vibe can run on CO2 and HP, and the Ion can be upgraded to tournament level. These three guns will run you about $100-200. BUT you can find used Ions with upgrades for around $150. Try PBnation.com for used guns.
a new feed neck or a drop forward
An MR1 is a decent started gun. They are easy to fix and not nearly as expensive as most markers. They also have a great scenario looking gun. Though, for the price you pay (around 100) you may as well but a Smart Parts SP1 or Vibe or a Tippmann 98 Custom. Or better yet, add a few more and purchase a Smart Parts Ion or Ion Xe. Spyders are good guns, do not misunderstand, but they are so easy to fix because they break down very easily.
An Ion is short for the marker, the smart parts "ION." It is an electro-pneumatic marker with impulse barrel threads, ion feedneck threads, and reverse threaded regulator threads. The classic ion cost about $200, where the new ION XE costs about $220.
Smart Parts (Now GoG) made mid level electronic guns. The Ion series (now eNMEy) was a popular, relatively inexpensive speed ball marker with huge customization and potential for high fire rates. The SP1 was an Ion with a more tactical looking rugged exterior and good customization for woodsball. Both series were relatively cheap for high fire rates but lower reliability.
Anything that fits in the standard feed-neck. So no A5 cyclone feed tops.
Online, or at any place that trades or buys markers.