I want to re-arrange my bathroom, by moving the toilet to the other side of the room, and moving the bath under the window (where the toilet currently sits). Is this something that can be achieved (ie with having to re-route the waste pipe etc), and if so does anyone know how much I may be looking at paying for a plumber.

Loaded question. Depends how much he charges. Generic. Probably yes the line will be rerouted.The plummer now has to determin If he can get enough slope to the new toilet location to the existing soil line. Now he might have to put a new vent to the new tiolet. Now for the tub this will be a two line waste and tied into the existing line. Here's the problems we run into the field. Do we have enough fall to the main line. Is the main line below the joist bay. Do we need to box out the a joist and double up on the joist. Is there enough room below the joist to drop the whole 3" sewer line to get the fall thats needed. Are we working in cast sewer line and it that area in the bathroom needs to changeto P.V.C. Are the water lines old and are the Galv or old black iron pipe and then he needs to get back to a threaded spot on both lines and switch to CPVC or your area might sill require copper supplies. Is here a way to use the old vent or does a new one need onstalled and run up through the roof? Here is the one I hate. The new toilet location hits right on a joist and how much does it hit. is there enough room to use an offset closet flange to get away from that joist? "recapp" fall, vent, cast. balck iron, water supply. To answer that question A ruff in and fnish on the plumbing could be $2,000 to $3,500. I do prof plumming and it easy for me and my guys. The home owner can possibly do there own if they are skilled and have the right tools and information. In most cases most can not or can due just a little. For Example A toilet ruff in is 12" from the finish wall to center to closet flange center( The johnny bolt location) Now that 12" from finish wall and not the baseboard but the whole wall. Now how plum is the wall so the tank lid will fit. I am going on too much sorry. I hope this helps you and have a nice Holiday P.S. this is just the basic

Cbell, since you know you will need to hire this job out just call 3 plumbers for a free estimate. This is far more accurtae than we can tell you without seeing your home. The switch should be doable since there is enough slope in the current drain line but you won't be able to reuse those drain pipes. The floor must come off or maybe the work can be done from below. The toilet needs at least a 3" drain with a 1/4" slope per foot until it reaches the main drain. Your current sink drain is likely 1 1/4"

I agree call a plummer I forgot to add that just because you have slope now doesn't mean the change is easy. If the 3" soil line has slope now doesn't mean is awalys doable. If the soil line has to be jumped into another joist bay and your on a sceond floor many times a small soffit has to be built because you can't just start drilling 3" holes in the wrong part of the joist and weaken it or too much to box in If the soil line heads towards and down the outside wall and down in and old solid bricks home it gets very involved. And it gets real expensive Its more than just a slope.

Are you on slab or raised foundations?

If on slab, it is messy and costly. If on raised foundation, it is lot easier. Also, it it easier to work with plastic pipes than Cast Iron. Costwise, it depends where you live. Here in So.Cal, you would pay around 3K for labor / rough materials only. You supply the fixtures.