This is my attempt to build a machine that was fast and accurate for less than £100.00. I've more or less achieved that but you need to shop around for the parts and the Igus samples service helped a lot when it came to the bearings for the X, Y and Z carriages. That said, with a group buy, it comes in at the budget even if you purchase the bearings. The reason for using them was to enable me to use cheap rods for the carriages. I used 8mm and 10mm OD steel tube from a local DIY shed but you could use aluminium, or anything really. The core xy lines are 100lb spectra fishing line and it runs on bearings throughout. There is a full video walkround of the completed machine here http://youtu.be/_oyftJF3l34.
I've added a better quality video here :-
http://youtu.be/QpjG7UqW8mI

BOM
1 x RAMPS 1.4 (or similar XYZE 3D printer controller)
4 x NEMA 17 stepper motor
1 x 12v 6A power supply unit
3 x miniature micro switch (limit switches)
1 x J Head (complete with 500mm PTFE & two 1/8 NPT 4mm pneumatic fittings)
1 x 50mm centrifugal fan
8 x 2020 extrusion @ 310mm I
4 x 2020 extrusion @ 400mm
2 x 8mm OD tube (or rod) @ 310mm
2 x 8mm OD tube (or rod) @ 350mm
2 x 10mm OD tube (or rod) @ 400mm
1 x M8 threaded rod @ 400mm
2 x 20mm aluminium angle @ 300mm
8 x 625 bearings (16mm x 5mm x 5mm)
8 x 623 bearings (10mm x 3mm x 4mm)
4 x 608 bearings (22mm x 8mm x 8mm)
8 x Igus 8mm bearings PN JFM-0810-10
4 x Igus 10mm bearings PN JFM-1012-15
5M Spectra 100lb fishing line
2 x 30mm tension springs for Greg's Wade extruder clamp
4 x 20mm tension springs for base plate
17 x M6 20mm dome head screws
30 M5 10mm SHCS
2 M5 60mm SHCS
16 x M3 8mm SHCS
6 x M3 10mm SHCS
18 x M3 20mm SHCS
1 x M3 25mm SHCS
4 x M3 25mm countersunk
2 x M3 50mm SHCS
2 x M5 nuts
30 x M5 half nuts
42 x M3 nuts
4 x M3 Nyloc nuts
3 x M8 nuts
Various M3 & M5 washers
1 x 250mm x 250mm x 6mm acrylic base plate (or anything suitable)
1 x 20mm x 50mm x 6mm UHMW polythene sheet Z leadscrew nut (drilled 6.25mm tapped M8)