To composts in order to kill bad microbes it has to be at 120-150 degrees. After the initial mixing, compost pile will heat up quickly, staying hot for several weeks or a month. When it stops steaming it is ready.
If you do not have all the materials needed to heat it up to the point of steaming you have not even started.
It is possible to re-use the soil with out composting. However you run the risk of problems being passed on if there were any in the prior grow. If there were no problems then you probably would be fine.
Now let us talk about your buget for soil; stop buying pre-made soil with someones name on it.
I go to my local dirt and gravel store and by their potting soil mix. http://www.acmesand.com/topsoil/ 1/2 a cubic yard is about 100 gallons so that is $32 where I buy it.
Then add worm castings (the most expensive if you do not grow your on)
EWC with the compost is a good enough with teas however you can just top dress like you mentioned also.
Here is a place in california with soil premade in bulk all costs are really cheap.
http://www.kinneynursery.com/landscape-soil.html the Barnyard mix does not look too bad. 100 gallons $21 and your down the road. Get any toppings you want for about another $30 and you should be able to grow 35-45 plants for about $50.
Invest in buying some compost and ewc for teas and you should not even need dressings.