price to install techo-bloc flagstone
1 Just the stone for a flagstone patio can cost $3 -$5 a square foot or more, depending on location and the type and quality of stone, or about $600 -$1,000 for an average patio up to 10'x20,' and $1,200 -$2,000 for a larger 20'x20' area.hopping for a flagstone patio: 1  Many contractors recommend sealing outdoor flagstone to preserve the stone and give it a more colorful wet look. 2  Sealant averages $30 -$60 a quart, or $100 -$200 a gallon; stone cleaners run $10 -$40 a quart.