Yes and No.
Some waxes are "all temp" and they are classed as universal so can be used in any temperature.
Some waxes are temperature range specific and the are typically broken down into three ranges.
These are just a guide to the temperature break points.
Spring - For warmer temperatures around 0° and above.
Standard - For average resort temperatures from -7° to 0°.
Cold - From around -7° and lower.

The best way to look at it is "How many full days on the snow" and we would say if you are going on a holiday with natural snow, you should be able to get the full 6 days without a big drop in the performance of your base. Unfortunately it's never that simple so when you factor in ice, man made snow & how long on/off piste it's almost impossible to advise.
We would give a simple guide of a week holiday will be fine if you do a good wax job before you go but if you're a speed demon, you can use a rub on wax to give you a boost for the last 2 days.
If you are lucky enough to do a 14 day holiday we would suggest you get a local tech to wax your base midway through.
If you ride UK indoor snow it's all about base protection, the quality of the snow in our snowdomes is not great so I would say 6 hours of slope time and you will need to wax again.

Yes a £10 cheap iron will do the job but has a thin base plate that can't hold the required temperature for more than a couple of seconds.
A £30 dedicated wax iron will give you a much better job and it has its settings in degrees so you can set it to exactly the required temperature for the wax you are using.
£50+ wax irons have a much thicker base so they can consistently hold the exact temperature you need, it sits in the sweet spot and that makes waxing a doddle to master.

We have added a great video for this at the bottom of the page and remember that ski ties are cheap and really help.