When I get most new balls for $70 or less shipped to the door off here or ebay, or bowlingball.com, and drill them myself its almost as cheap.
If you get a ball used for $30-$50 shipped to you and plugged it completely and have it redrilled your looking at $30 in plugging and $10-$30 in finger inserts and thumb inserts? So up to $60+ tax for a complete plug and redrill with inserts.
Or if you just plug the thumb and redrill it with a slug thats maybe $10 for plug and $15 for the slug so $25 + tax on whatever the ball cost.
It can be expensive. Granted for many if you have to pay to have your new ball drilled ,that was purchased else where, some places will try and screw you that way as well.
For me I take new over used.
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" men lie, women lie, numbers don't "