I was just wondering since I can't easily find a 250 watt S50 HPS bulb.

In many cases, if you do not modify the ballast, a North American 250w M58 probe start metal halide lamp and a North American M138/M153 pulse start metal halide lamp will be overdriven on a North American 250w S50 high pressure sodium ballast. In addition, if you leave the ignitor connected to the lampholder, there is a good chance that you will destroy the starting probe or starting resistor of a North American 250w M58 probe start metal halide lamp if you use that lamp on a North American 250w S50 high pressure sodium ballast. There are also some 250w metal halide lamps that will actually run fine on a North American 250w S50 high pressure sodium ballast. Some examples of such metal halide lamps would include an Osram HQI-T 250W/D, the GE 250w Chromafit quartz and ceramic metal halide lamps, a GE 250w ArcStream metal halide lamp, a Venture Whitelux 250w metal halide lamp, etc.

On eBay, it is pretty easy to find North American 250w S50 high pressure sodium lamps. Just type in “LU250” in the search box and plenty of North American 250w S50 high pressure sodium lamps will pop up in your results.

In many cases, if you do not modify the ballast, a North American 250w M58 probe start metal halide lamp and a North American M138/M153 pulse start metal halide lamp will be overdriven on a North American 250w S50 high pressure sodium ballast. In addition, if you leave the ignitor connected to the lampholder, there is a good chance that you will destroy the starting probe or starting resistor of a North American 250w M58 probe start metal halide lamp if you use that lamp on a North American 250w S50 high pressure sodium ballast. There are also some 250w metal halide lamps that will actually run fine on a North American 250w S50 high pressure sodium ballast. Some examples of such metal halide lamps would include an Osram HQI-T 250W/D, the GE 250w Chromafit quartz and ceramic metal halide lamps, a GE 250w ArcStream metal halide lamp, a Venture Whitelux 250w metal halide lamp, etc.

On eBay, it is pretty easy to find North American 250w S50 high pressure sodium lamps. Just type in “LU250” in the search box and plenty of North American 250w S50 high pressure sodium lamps will pop up in your results.

Can I remove the starter to run a probe start MH bulb?

Can I remove the starter to run a probe start MH bulb?

You can remove the ignitor for a probe start metal halide lamp, however, since North American 250w M58 probe start metal halide lamps run at 130v 2.13a and North American 250w S50 high pressure sodium lamps run at 100v 3.0a, you might shorten the life of your probe start metal halide lamp since the lamp would be drawing substantially more current than it is designed for unless you can find a way to modify the ballast in such a way that would allow your 250w probe start metal halide lamp to run at its rated current. In order to experiment with alternative ballasts, I recommend getting a clamp meter since it is an instrument that measures how many amps your lamp is drawing from the ballast that it is being used on.

How much shorter will it's life be? I just need an alternative for it until I can get some HPS lamps.

IIRC there were a few drop in MH and even CMH replacement bulbs for 250w HPS but those are probably a lot harder to find than a 250w HPS lamp. Philips made a CMH like that.

eBay does have some for real cheap. I saw one for around $9 with free shipping .