I'm no expert by any means but I have fixed similar myself (although it took me ages and it is not a wonderful job). This should be no big thing for a carpenter or even a decent handyman. It shouldn't cost too much or take any longer than a few hours at most. I did mine with stuff from B & Q.
Now if you want to go double glazed you can but usually these are made of units in a factory and then fitted whole. If you tried to bodge it you probably could but I have a suspicion that it wouldn't be massively easy to get the right seal etc. As if not sealed properly there is little point to double glazing. Plus you have the obvious problem of fitting the glass.
My guess for fixing is only around 100 quid but a new double glazed window may be a few hundred.

Red and Blue Army!

Sorry ASCPFC if I'm being a bit dense, but are you talking about having replaced the whole lot, or just the hanging bits (oooh - sounds rude!)?

Palace since 19 August 1972. Palace 1 (Tony Taylor) Liverpool 1 (Emlyn Hughes)

I pulled out the rotten parts of the frame. Roughly measured the wood I needed. Got that wood, some filler and some beading, and cut the wood roughly to size then fitted it back into the frames (making adjustments with chisel and plane whilst I fitted). I then pinned and glued the beading in which had a double effect of holding the glass in firmer. Now this took me about a week (with many, many breaks and much swearing). I had to replace glass as well but the wood, tools, beading etc were certainly around 40 quid. Glass is surprisingly expensive and comes in all kind of finishes
I tried to but the cheapest but got toughened just to be safe. I think glass was 150 or so!

Red and Blue Army!

Reading your original post I told you what you knew, yes the part that opens I do believe is the casement.

We had some wooden ones made and they were at least twice the price of uPVC. Then we found that nobody near us gave a damn about the rules and wouldn't have complained about uPVC or aluminium.

The one on the left looks bodgeable with a good rub down, rot proofing and filler. I reckon you could get a few more years from it. The one on the right looks dodgy but I do think a carpenter would be able to do something with it.

Take a look at this, maybe both can be recovered for a while

[Link]

Edited by Mapletree (15 Jul 2019 5.43pm)

From the photo the outer frame looks in good nick. It’s hard to see from the photograph but From.a builders point of view there are two ways you can go, If you didn’t want to replace the casement windows and you want a repair then you could buy liquid wood hardener from DIY, builders merchants. Take the casements windows out, if you can rub them down and then paint the wood hardener all over the rotten areas. In this sort of case I would apply two to three coats of harder leaving a day in between. Then get a good quality wood filler, Ronseal wood filler is a good one easy to sand, then Depending, if the outer and casement frames are hard wood I would paint them with an aluminium primer then undercoat and gloss. If the frame is soft wood personally I would paint 2 coat primer 2 undercoat, top gloss, but I would use a weather shield undercoat and gloss.
The next step you could is find a joinery shop and ask them to give you a quote, I’ve done quite a lot of these in the past and the joinery shop will obviously take into account the shape of the window it basically down to you and what you want if you repair it’s impossible to say how long it would last that depends on how good the workman is.

South London & Proud
Sometimes I really wonder if family are really worth it.
Because it doesn’t matter how time and affection you give
It’s never enough

You could always leave it until the last minute and simply paper over any cracks.

Red and Blue Army!