Help with soil problem!

So Im wanting to start growing my 15 plants this friday.
But I dont know how much soil I should expect to buy for my 15 plants.
I have no idea how much soil costs these days, but Im planning on digging big holes (maybe 3x3x3)
I no thats 27 feet but how much do bags of soil cost? and how much does a bag fill?
If anybody knows a store that sells cheap but efficient soil let me no! (wal mart, lowes, menards)
Will 60$ be enough for 15 monster plants or am i way off lol
Also how much is perlite? I no I should just go check out the stores myself but I really wanna save a trip to the bank.

60 might be enough to get 1 monster plant. lol surely not 15 though man. figure for good soil and good amendments you'll spend anywhere from 30-60 bucks a hole. each of my 2x2x2 holes is running right at $30 and I cut a couple corners. (I might but might not regret) My teas should help out there if not I got the high power nutes on stand by in the closet. hoping and praying to not have to use them as this year im trying to go all organic for the first time.

The best potting mix right now is probably Roots Organic which goes for $25-$30 a bag. Fox Farms and Sunshine Mix #4 average $15-$20 a page . Scott's Super Soil is about $7 a bag and on the west coast you can buy my favorite soil which is Kellogg's Patio Plus and it sells for a measly $5 a bag. All bags are usually 1.5 cu ft. For a 3'x3' 2ft deep raised bed, which is what I built, expect to go through about 10-12 bags. A 3'x3'x2' area is perfect for one large bushy sativa. For monsters get them in the ground early and space them 10'-12' apart.

go get some compost soil from your dispensery and add some admendants you will spend 20 on composted soil thats organic for one trckload and bat guano worm castings ext like 80 - 100 bucks you got it all good but also i recomend happy frog mix it with ocean forest mix up if you wana spend some cash you will b good to go then after about a month an 5 days make some organic teas and you sit back and watch mother nature do her job