The ingredients are cheap and better yet, you can find them at any garden center or any decent hardware store that has a garden section. The "compost" can be home made if you like, but the "topsoil" should be store-baught (no "backyard dirt"!).
The basic soil mix:
1 part Compost.
1 part Topsoil.
1 part Vermiculite and/or Perlite.
1 part Composted Steer Manure.
To each gallon of soil mix add:
1-2 Tblspns. of Dolomite Lime or Garden Lime (depending on final Ph).
"1/2 Dose" of Dry, "Meal based", All-Purpose fertilizer*.
* I have used FoxFarms "Marine Cuisine" (10-7-7), Whitney Farms "All-Purpose" (5-5-5), and Kellogg's "All Purpose" Organic (4-4-4). Anything similar to these products should work fine. The main thing to remember is you only want to use at 1/2 strength according to the package directions for "Potted Plants".
If you're mixing a "big" batch, pour the ingredients into a hard plastic "Kiddie Pool" and mix it up with whatever kind of hand tools (hoes, shovels, etc.) you have available. Add only enough water to eliminate the dust. Mix very well!
Add the ingredients a little at a time and alternate back and forth between the ingredients (a little topsoil, a little compost, a little Perlite, a little manure - mix, mix, mix - then start all over again - etc., etc.). Mix the Lime and the dry fertilizer in with the first or second "round" of ingredients, so they get well mixed into the whole batch.
If you're just mixing enough soil for a few small pots, use an appropriate sized scoop for each "part". You can use a "cup", or a 4" or 6" pot, whatever! Just scoop the ingredients into a 5 gallon bucket (no more than 1/2 full, less is better!). Now tilt the bucket at about 45 degrees and turn it (like a cement mixer). Add only enough water to eliminate the dust. Add the Lime and dry fertilizer early in the process so it gets mixed in well. If you have 2 buckets, it is also helpful to "pour" the mix back and forth between the buckets (alternate the "pouring" and the "mixing" for best results!).