Here are some ideas for cheap & easy crafts to make with kids on the topic of prayer:
1. Praying Monkey
2. Jelly Bean Prayer Jars (includes free printable cards)
3. Prayer Buckets
4. Prayer Rocks (has some neat ideas for how to use these to remind kids to pray)
5. Prayer Garden (this one takes a bit more work, but with beautiful results).
6. Prayer Journal (instructions are minimal, but you get the idea!)
These crafts work great with 10:10 Kids! Teach Me To Pray 4-week Bible lesson plans.