So you have a house, and you have a yard, and you want to know how to make them work in harmony, but you don't want to break your wallet, well leys look at exactly what your gonna need to do it.
1 - a shovel, Because just because its cheap, doesn't mean your not going to have to work for it.
2 - a hole saw
3 - a rope, string, twine, something long, at least 100 feet, that you can use to mark your path
4 - a phone
5 - 72 feet of 4 inch PVC piping, sold in 8 foot sections
6 - four 45 degree angles for 4" pvc pipe
7 - four 90 degree angles for 4 inch pvc pipe
8 - about a dozen 4" to 4" pvc couplers.
9 - pvc glue
10 - two 4 inch computer exaust fans
11 - a good weekend of nice weather.
All in all the materials should run you less then 100 dollars, which while it's still no chump change, isn't all that hard to save.
Now I'm going to be using my house as an example, but if you don't have a basement, you at least have a crawlspace, and this is going to require getting under your house. You're going to want to choose a room that has two air vents, as your going to be using them, unless you want to cut 2 holes in your wall.
Your going to have to use the rope to mark out a distance straight away from the wall of the house about 35-40 feet, then turn 90 degrees, measure another 8 to 16 feet, and turn 90 degrees back to the house. The trick to this is, the short side needs to be the same distance as the air vents are, because the pipe going away and the pipe coming back are going to connect up to those vents. Once you have your string/rope/etc laid out, get your shovel. Your going to need to dig the entire length of that rope, from the wall of the house to the bends, then back to the wall of the house. This hole needs to be at least 30" deep, to clear the north american frost line. Once you have it dug, take a break, that was a lot of work!
Next your going to connect the pipe together using the couplers, angles and glue, this part should be pretty self explanatory. The difficult section is using the pipe next to the house, you'll need two 90degree angles to bring the pipe up, then a 45 degree angle to take it into the crawlspace or basement, through the wall. Once inside connect the other 45 degree to level the pipe out with the floor above you, so you can extend it to the location of the vents.
Remove your vent covers, and insert a 90 degree bend into the vent, facing outward and down, this pipe will be hidden when you put the cover back on, but don't do that just yet. go back under the house and cut your 4 inch hole in the ductwork so you can use a length of pipe to connect the two angled together, Don't forget glue! Seal any gaps in the duct with tape for an airtight seal.
Go back up stairs, and place the fans over the pipes in the air vents, you want one blowing into the pie, and one blowing out. Wire them both to a plug close by, and replace our air vent covers. Air will now circulate through the pipe, colling as the heat is leached into the ground around it, dropping to a nice comfy 65-70 degrees before blowing back into the house. After several days, it should have lowered the ambient temperature in your house significantly, decreasing the need for an energy consuming air conditioner. The best part is, the fans will use less power then a light bulb to run!