The key goal of any brew enhancer is to help the beer have more body, a great taste and good mouth feel. If you just use sugar for the yeast to feed on, you will get a thin, weak beer. Of course you do not need to buy brew enhancer, you can make your own. There is no right way to prepare the enhancer as different ratios and different ingredients can produce different effects on your beer.
If you are going to make your own enhancer, here’s some ingredient ratios which you could use as a guide:
Ale, more malty beer
The quantity to make is is 1Kg per 23 litre brew.
The beauty of using the dextrose is that it is apparently a more favoured food of the yeast when compared to ordinary sucrose sugar and so fermentation will commence more quickly. Whether that makes a difference to the end result, I don't know.
You do not have to follow the above guide - you could simply make a 50/50 split of DME and brewing sugar (which is simply corn sugar). Many beer supply shops will carry the ingredients you need. That way you can get the advantage of buying in bulk so to reduce your brewing costs. Check out the price of DME on Amazon.