Is a 3-D printer made from 3 CD Drives practically somewhat decent, being DIY and less expensive?
I would guess that a printer made in the following way would be both poor quality, and annoyingly frustrating, as well as requiring constant tinkering/re-adjustment. Also, if the chassis of the CD/DVD drive is incorporated into the design (as below) then the print volume is rather small, given the inherent limited movement of a CD/DVD mechanism. 

If the steppers are used without the CD/DVD chassis then it might be possible to increase the print volume but then you would need to spend extra on the rods and support structure for the X gantry, the Y-axis print bed, and the Z-axis movement. If you do that, then the steppers from the CD/DVD drive probably would not have sufficient torque to move the additional weight - by incorporating the CD/DVD chassis the inertia of the movement has been kept to an acceptable minimum.

By using the CD/DVD drive's stepper motors you are only really saving the cost of buying three or four actual, more powerful and useful, stepper motors (as well as the cost of the additional rods and support).

That said, it could be quite amusing to make, and show off, and also provide some satisfaction if you do manage to print a tiny frog, parts for another printer, or whatever, with it.  However, I wouldn't expect it to print anything to any great accuracy/tolerance/precision/etc., but it would maybe give you something unusual to talk about at dinner parties.



An example

There is this (IMHO unjustifiably1) popular (i.e. well linked-to) Instructables guide: EWaste 60$ 3DPrinter, which describes making a 3D printer from old desktop computer parts2.


  $ 3DPrinter"> 3DPrinter" title="EWaste 60$ 3DPrinter">


According to E-waste printer looks nice, prints really, really small, it has an awesome print volume of  37&nbsp;mm x 37&nbsp;mm x 18&nbsp;mm.

Apparently, all you need is to salvage:


2 DVD drives (Matsushita stepper datasheet)
1 floppy disk drive (ensure it has steppers and not simple d.c. motors)
1 PC power supply


Then purchase these standard 3D printing components:


RAMPS &amp; Arduino Mega or RepRap Gen6/7 - Capable of running Marlin/Sprinter frimware
Nema 17 stepper motor for the extruder - Either this, or better still something from RepRap Wiki - Nema 17, i.e. Kysan 1124090/42BYGH4803, Rattm 17HS8401, or Wantai 42BYGHW609.
MK7/MK8-type direct drive gear for extruder
PTFE tubing
Hotend (throat, heaterblock, nozzle)
Heater
Thermistor
Cables, female connectors, heat-shrink tube.


To make the frame, you need a 325&nbsp;mm x 362&nbsp;mm, 5&nbsp;mm thick acrylic sheet, and use this template (missing files):


  


or this one (cnc-calisma-yalniz.dwg):


  


You will also need to 3D print these parts (the links to which have died):


Extruder idle
Extruder body
Hot end holder


Once you've gathered all of the parts required, you can then try to work through the incomplete assembly steps of the Instructables guide.



Other links


A very similar printer also made from an old DVD drive, Instructables: Curiosity 80\$ EWaste Educational 3D Printer. See also An E-waste 3D printer for every child?
A very complete, and IMHO, a much more doable E-waste printer, Instructables: Complete Newbie Step by Step, 3D Printer With All Parts Lists
Other Instructables, that I've not really looked into:


Super Cheap 3D Printer From CD-Rom Drives
Cherry- 60€ 3D-Printer
Poor Man's 3D Printer
Chimera: \$60 DLP High-Res 3D Printer
3d Printer for Less Than \$100 USD!!!
A Low Cost 3D Printer With Basic Tools

Thingiverse: \$65 3D printer made from recycled electronic waste




Footnotes

1 Most, if not all, of the links for the printer above are dead (this variant, mentioned above in Other links, is much more complete). However, with a bit of knowledge, and common sense, it should be possible to work through those omissions:


Marlin software - easy enough to find on Github
The frame laser cut - the original file is missing but an alternative is still available
The 3D printed parts for the extruder - as the links have died, you'll either need to find reasonable facsimiles on Thingiverse, which shouldn't be too hard to find, or buy them from cheap Chinese suppliers:


Extruder idle
Extruder body
Hot end holder



2 Funnily enough, whilst searching around looking for information to fill in the gaps in the above answer, I found this question on 3DP.SE: Missing print steps in e-waste 3d printer