Going to need a LOT more info than that for ANYONE to venture a guess.

It can be a little or an aweful lot depending on a lot of things that remain unknown to everyone but you.

The shower is fitted. It is a small hole about half a cm, directly down from the drain in the plastic pipe. I don't know what other info to give

Is there a finished ceiling below it. Or open floor joists... is it on a cement slab?

No one can tell you how much it will cost. It all depends on what plumbers in your area charge and how long it takes. Proper repair will involve cutting the pipe at the hole and then reconnecting it with a coupling. How long that takes depends on how difficult it is to reach and whether the pipes will move apart after you cut them in order to put the coupling on.
A temporary repair might be to put something soft, like rubber over the hole then clamp it in place with a band clamp.

HI Kirstie...

Is the pipe accessible from underneath? If the pipe is accessible from underneath then it shouldn't be a real big deal to cut it out and replace it. I won't venture a guess on cost as costs vary dramatically, but the job shouldn't take a plumber more than a couple hours to complete from start to finish (including travel time).

If the pipe isn't accessible then the job grows more difficult, for sure!

If you can see the hole why don't we see if you can do a repair on this yourself, although it will be more of a patch job than a repair, OK? Here, I would recommend that you purchase a PLASTIC EPOXY PUTTY (see images) at a home improvement store. Come home and empty the shower drain of water if the water will interfere with the patch job. Then, stuff a rag into the drain (tied onto a string) past the hole just in case you drop something in the drain. Next, take some isopropyl alcohol and a cotton ball and clean the area to be patched. After that, knead the 2-part putty until the two parts blend properly and then push the putty into the hole. Smooth the putty edges smooth to the pipe walls and let it dry per instructions on the tube. For best result repeat these steps with a second patch, again, feathering the edges tight to the inner pipe wall. Let it dry and check your work. With any luck it will last years... ;)

You may also want to try this with a silicone sealant/caulking being sure to pre-clean the pipe for best adhesion. You would do this on the inside and the outside of the pipe if the pipe is accessible.In my opinion, however, the epoxy putty plastic patch will be best result.

Questions? Let us know, OK?

Mark

Hi Guys...

I was typing while you were all posting... *UGH*.

Your questions and ideas as always are more than reasonable!

Mark