Wouldn't you expect a carbon tax to be similar in price to the cost to get the carbon back out of the air?
CO2 released per barrel of oil (when converted to various fuels and burned) appears to be around 300-450 kg [1][2], but we can round up to 500 kg to be conservative and make the math easier.
The cost to take it back out of the air appears to run between $30-$200/tonne depending on how you do it [3][4][5]. I think it's worth speculating that this cost is likely to drop precipitously as the demand and scale at which we need to do it increases, but we can very conservatively stick with $200/tonne for now.
Crude oil is at about $59/barrel today. $200 * 0.5 tonnes = $100. So with the most conservative estimates, it wouldn't quite triple the cost.
[1] https://pyrolysium.org/how-much-co2-produced-by-burning-one-...
[2] http://numero57.net/2008/03/20/carbon-dioxide-emissions-per-...
[3] https://www.c2es.org/document/the-cost-of-u-s-forest-based-c...
[4] https://cleantechnica.com/2016/01/19/carbon-capture-expensiv...