If by costs you mean how much u need to pay to enter it should be much less usually only 5% for the margin.
If by costs you mean potential losses well that can be controlled by how much you buy. 20k is a tone of money to have in CFD's as it is way more expose than 20k in shares (im talking about margin here). I would usually go about 10 to 15 times less. I usually trade in 10k lots so i would invest about 1k or 2 in equivalent CFD's and get about the same if not more volatility.
