These are the most popular platinum and iridium plugs
Denso Iridium Ik16 $11.99
0.4mm Iridium Center Electrode, Tapered Cut
U-Groove Ground, Resistor, .044" Gap
Ngk Iridium Ifr5e-11 $11.71
Resistor, Projected Tip, Extremely Long Life
Plug, Iridium Center Electrode With Platinum
Tipped Ground Electrode, .044"Gap
Ngk Platinum Oem Pfr5g-11 $11.71
Resistor, Projected Tip, Extreme Long Life Double
Platinum, Fine Point Platinum On Center
Electrode, Platinum Tip Laser Welded On Ground
Electrode, .044"Gap
Champion Iridium 9201 $8.11
Resistor, Projected Tip, Extremely Long Life
Plug, Iridium Center Electrode With Platinum
Tipped V-Trimmed Ground Electrode, .040"Gap
Ngk Iridium Ix Bkr5eix-11 $6.95
Resistor, Projected Tip, Fine Wire (0.6mm)
Iridium Center Electrode, Tapered Cut Ground
Electrode, .044" Gap
Denso Double Platinum Pk16pr-L11 $6.82
Projected Tip, Resistor, Double Platinum,
.044"Gap
Champion Double Platinum Rc12pyp $5.47
Double Platinum, Resistor Plug, Projected Tip
Autolite Double Platinum App3924 $5.30
Gasket Seat, Resistor, Power Tip, Copper Core,
Double Platinum
Iridium
Iridium is a precious metal that is 6 times harder and 8 times stronger than platinum, it has a 1,200=F higher melting point than platinum and conducts electricity better. This makes it possible to create the finest wire center electrode ever. Prior till now, spark plug manufacturers have favored platinum for their long life or performance spark plugs due to its high melting point, also the technology did not exist to machine and bond iridium on a spark plug electrode (at least in a cost effective manner). Champion spark plugs have produced iridium industrial and aviation spark plugs since the 1960's, but they still sell for over a hundred dollars per plug. Just now is the technology cost effective to use iridium in a spark plug for automotive applications. The strength, hardness and high melting point of iridium make it very well suited for a fine wire plug. The primary iridium plug manufacturers at this time are Denso with a 0.4mm center electrode, while Champion and NGK have 0.7mm center electrodes. These are the best performance plugs on the market for traditional automotive use and many racing applications. Autolite has introduced an iridium-enhanced plug (the iridium content is too low to call it an iridium plug) we do not consider this in the same class as Denso, NGK or Champion.
SIDENOTE: Thus far the tech's we have spoken with report no problems using iridium plugs with Nitrous.
Platinum
PLATINUM'S USE IN SPARK PLUG CONSTRUCTION
Nearly all spark plug manufacturers use platinum in one form or another on their long life or performance spark plugs. This is because of platinum’s high melting point which makes it useful in two ways. On long life spark plugs a thin wafer of platinum is bonded at the firing point to the center electrode (and possibly ground electrode) solely so they don’t wear as fast as a traditional plug. On a fine wire performance plug, the very tip of the center electrode is made of platinum so that the fine wire tip will last longer. Do not be fooled, all platinum plugs are not created equal, Platinum is a very expensive precious metal, a $2 platinum spark plug will not have much platinum in it, and therefore will not last as long as a $12 platinum spark plug. Some platinum plugs have only the center electrode tipped with platinum, while others have both the center and ground electrodes platinum tipped. (it is not suggested that platinum plugs be used on vehicles with nitrous injection, there have been no problems reported using iridium plugs with nitrous).
Resistor
At the moment the spark jumps the gap it causes a high frequency burst of energy, this is known as RFI (radio frequency interference). This is why resistor spark plugs were introduces in the mid 1960's. Placing a resistor within the spark plug suppresses the RFI. Without resistor plugs in your car you can experience static on your radio as well as interfere with other sensitive electronic equipment. Some later model vehicles as well as newer Powersport engines must use resistor plugs for a proper "talkback" to the electronic ignition. Outboard marine Capacitive Discharge Ignition (CDI) such as used on some Johnson and Evinrude marine engines require a special inductive type resistor (such as a Champion Q-type or NGK Z-type). Use of non-inductive resistor type plugs on these motors can cause misfire and poor performance.
For automotive CDI high output ignition systems systems (such as Mallory, MSD, Crane and Accel), refer to Resistor plugs for race engines for information relative to modified motors.
When should I use a resistor spark plug?
"R" or resistor spark plugs use a 5k ohm ceramic resistor in the spark plug to suppress ignition noise generated during sparking.
NGK strongly recommends using resistor spark plugs in any vehicle that uses on-board computer systems to monitor or control engine performance. This is because resistor spark plugs reduce electromagnetic interference with on-board electronics.
They are also recommended on any vehicle that has other on-board electronic systems such as engine-management computers, two-way radios, GPS systems, depth finders or whenever recommended by the manufacturer.
In fact, using a non-resistor plug in certain applications can actually cause the engine to suffer undesirable side effects such as an erratic idle, high-rpm misfire, engine run-on, power drop off at certain rpm levels and abnormal combustion.
Prices are according to this website
http://www.sparkplugs.com so may it be lower or higher depending where you buy them i wrote it so you guys have an idea of the cost between each one.