There is an opportunity to volunteer for a daylong which allows you attend that event for free. Also all retreats offer a few volunteer spots that allow you attend the retreat free by helping out only a few hours a day. Check website for details.
Many events are free and open to the public. Some events cost money and you need a reservation. For the most up to date information check their calendar at www.spiritrock.org. I personally have only attended residential weeklong retreats which cost about $1200-$1600 which includes meals and lodging.
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