I would hesitate on the mushroom compost. Do find out what they use to grow the mushrooms in. We have a mushroom grower near here and they always offer the substrate for free if you load yourself or a $20 loader fee for them to dump a load in your truck. Very cool price, but the stuff is a bit ripe. My area smelled of horse poo for at least a week. If it is very clumpy, you risk burning your plants. A neighbor damaged here lawn by using it. Also, if you are planting root veggies such as potatoes, you may want to stay away from manure compost.
I would suggest getting a garden mix delivered in the huge bags and add "Sea Soil". I love the Sea Soil for veggie gardens. It's a bit expensive here, but if you are near the West Coast, it is a lot cheaper...so I'm told.
