You should be able to purchase all you need for this for $15 or under and takes no more then 15minutes to sew up.

Here is the Mei Tai.. no action shots atm as my newborn is still in the making ;)
You will need
* usual sewing supplies.
* 1 fabric placemat, of average size (around 30X40 cm give or take), make sure the placemat is a sturdier one, a heavily woven one with secure edges or a fabric one consisting of 2 layers works well.. and there are ohh so many awesome designs around - the one used in this Tut was bought at Big W for $2-98. the other green and brown one was bought for $4 at spotlight.
* co-ordernating fabric. I use drill fo its sturdiness and strength, buy in a co-ordernating colour and purchase 1.5 - 2 metres of fabrics, best to by the full 2 metres if you arent sure what length you like your straps. This amount of fabric is actually enough for 2, so may aswell buy another placemat :D. I purchased the Drill for $5 pm from spotlight.
*prewash both the fabric and the placemat to save disappointment from a warped carrier after the first wash..
Lets get started.
CUTTING

*Cut from the full 2mt length of drill, 3 17cmX2mt strips. I used my rotary cutter. Dont worry if you dont own one. Scissors work fine, just takes a little longer

*Remove any tags from the placemat
MAKING THE STRAPS

*Taking 2 of the lengths of drill(these will make the shoulder straps), fold them longways ( making a rectangle 8cm by 2mtrs long)
*Sew along the length of the strip, then turning and sewing one of the short ends closed, be sure to leave the other open. I have used about a 1cm seam allowance, this isnt vital though.
*Do this with both strips, to create 2 shoulders straps

* Taking the the remaining strip, fold it, with both short sides together to find the middle point along the 2mtr length. Lay the placemat, folded in half longways over the top, lining up the folded edges.
*Mark where the placemat comes to on the strip, on both top and bottom side of the layers of the strip.

* Taking the strip, now folding it the same as you had for the shoulder straps. sew around the strip, sewing both short ends and along the long side, leaving the section between the marks you made, un sewn. This strip will be the waist strap.
* Take all 3 strips and turn them in the right way. Best way to do this I found, was over a broom handle
*Iron all 3 straps.
*For the shoulder straps, once ironed flat, take the open ends, tuck the raw edges in aboout 1 inch and iron these down.
*When ironing the waist strap the raw edges of the open section in to create a continual line with the rest of the seam and iron flat as well.
ATTACHING THE STRAPS

*taking the 2 shoulder straps slide the opened end over 2 of the corners of the placemat on a 45 Deg angle. pin Ensuring the edge between the 2 straps is a shorter edge, and this will be the top of your carrier so ensure if there is a direction to your design, you get it the right way around.

*Sew across the edges of open strap, sewing through both top and bottom layers of the strap and the placemat that is sandwiched in the middle, continue to sew over this 3 layered area criss crossing to reinforce the strap attchement, If you enlarge the photo above you can see how I have done so,

*For the waist strap, take the remaining short side of the placemat slotting it down into the section you left unsewn in the waist strap, Being sure to place it all the way down, so that the edge of the placemat sits right down in the fold. Pin in place.

*As with the shoulder straps, sew right along the open edge, through all three layers to close the waist strap. criss crossing back over the whole area to reinforce the strap. This reinforcing stitching may be better seen in the green and brown carrier at the top. Though feel free to stitch in what ever pattern you desire.

Snip threads and wear, it really is that quick.