That window looks like a pretty standard size (most big boxes stock 3 or 4 sizes of basement sliders). I just replace 4 of mine that were something like 16x32 or 16x31 with an off the shelf sliding/dual pane window from Home Depot. Each window was 60 bucks or so. I removed ALL the wood/framing from the old window to get to bare concrete. I then removed the panes from the replacement window, leaving me with just the vinyl box. From here, I dry fit the window in the old hole, flush with the inside of the wall. Now you need to locate the screw holes in the frame and mark them on the wall. It will probably be easiest to use your drill bit (masonry bit, of course, probably 5/32) to make a dimple in the cement in each spot. Remove the window, set your hammer drill to the appropriate depth for the Tapcon water resistant screw you're going to use, and punch the holes into the cement. put the window back in, shimming if you need to in order to keep it squared in the hole. Mind you don't create a bow in it. Cap the screw holes (probably came in the same packages as the screws), put the panes/screen back in, and head outside. Caulk around the window with some good exterior grade caulk (and be sure to have cleaned the concrete first with a wire brush or somesuch). Let this set for a bit, then use some non-expanding Great Stuff inside to fill in any gaps between the new window and the wall. If you use the regular expanding stuff, you run the risk of bowing in your window frame and causing it to not slide/open well. I leave enough space that after it's dried I can also caulk the inside with paintable caulk to give it a better finished look (or you could trim it). I have a cement/sloped sill outside my windows, so I painted those with a waterproofer and called it a day. Worked magnificently, and my basement is much less buggy/drafty.
Tools:
1. Hammer Drill (I did one with a regular Makita LXT drill, and it takes -forever-). If you don't have one, you can get a Makita LXT hammer drill with battery and charger for 99 bucks shipped from Amazon. Stupendous deal.
2. Tapcon screws (or some other masonry/water resistant screw). Probably 5 bucks for a box of 'em.
3. 1 can of non-expanding great stuff (might be the light green can? Just make sure it's non-expanding).
4. one tube of caulk - exterior grade, paintable.
5. caulking gun. 2 bucks for the cheap one, which works great.
6. shims - composite is the only way to go for a basement.
7. masonry bit. Buy 2, just in case. I have had pretty good luck with Bosch bits from Home Depot. The Tapcon box will tell you what size you need.
total cost, all in if you bought the drill and all is probably about $200. There is probably no need for a custom window as the dimensions on them haven't really changed. And if they have, you can usually custom order a basement slider for about double the cost of an off the shelf one, so you'd still be all in at about $250.
