If you are looking for a good quality pistol than I recommend looking into either TokyoMarui, KSC, KWA or Western Arms(WA). Each company is reputable and known for their quality of materials used in the production of each and every one of their items.
Prices vary depending on which brand and which model you select.
The majority of pistols run off of gas the others are either spring are electric powered. Spring powered guns require the slide to be cocked before each shot and generally only serve the purpose of shooting pop cans in your basement. Electric pistols or AEP are handguns that run off a small battery pack and use a motor to compress a small piston to drive air down a barrel which propels the BB. They generally function well but due to their smaller nature will not be able to match the output of that of a full sized airsoft gun. Finally we have gas based pistols, these come in the form of Co2 and green gas(propane) guns. Before I speak on the subject of gas powered pistols I would just like to clarify that green gas is in fact propane.
http://en.wikipedia.org/wiki/Green_Gas
http://www.airsoft-innovations.com/
Anyways back to the topic at hand. Gas guns store both the gas and bbs in the magazine of the gun when the trigger is pulled a small amount of compressed gas is released to propel the BB down the barrel. Essentially all pistols work on this concept, so the only thing that remains is for you to decide how you want your gun to look.
As stated above you may find yourself out gunned if you choose to bring a semi auto pistol to a full auto shoot out. Then I suppose you can say that its "how you play not what you play with". Actually that's a big pile of garbage, trying to take out 6 players head on who have more range, more accuracy and higher firing rate is ridiculous. Either way the decision is yours, you may wish to explore other options before you commit.
Best of luck.