Check your local phone book for wholesale clothing suppliers. You can get a price break from them because they deal in larger quantities. That way, you can purchase higher quality, name-brand tees, such as Haines Beefy Ts for prices lower than you can get low quality retail purchases of off brand shirts.
Each wholesaler will determine what their minimum purchas might be. Often, it will be as low as a dozen shirts. When I used to do custom airbrushed tees, my local supplier would sell me as few as a dozen, and would even let me specify sizes, styles and colors, mixed in that dozen.
Depending on your particular use for the shirts, sales tax may be an issue. If you plan to resell the printed shirts, you might not have to pay sales tax, depending on the rules in your state. IF you find a supplier, they should be able to advise you on this.
The answer to your question lies in understanding the spiritual significance of the word 'garment'. The hem of Christ's garment is but part of His outer garments and the most accessible.
The significance of wanting to touch the hem of His garment is that mustard seed of faith that tells us there is healing power within Jesus' body. It was Christ's white linens or garments that covered His body, and it would be His blood that covers our sinful and diseased flesh. When we come to Him seeking only to touch the hem of His garment, then, and only with that attitude, will we be cleansed, restored and reconcilated with God.
We come to Him with the attitude of the prodigal son, asking only to be a servant in the house of our loving Father, because we are now shamefully aware of our estranged sinful and humiliated condition. Luke 15:13-19
The story in Matthew 9:20-22, Mark 5:25-34 and Luke 8:43- 47 is a favorite of mine:
“As Jesus was on His way, the crowds almost crushed Him. And there was a woman there who had been subject to bleeding for twelve years, but no one could heal her. She came up behind Him and touched the edge of His cloak, and immediately her bleeding stopped. ‘Who touched Me?’ Jesus asked. When they all denied it, Peter said, ‘Master, the people are crowding and pressing against you.’ But Jesus said, ‘Someone touched Me; I know that power has gone out from Me.’ The woman, seeing that she could not go unnoticed, came trembling and fell at His feet. In the presence of all the people, she told why she had touched Him and how she had been instantly healed. Then He said to her, ‘Daughter, your faith has healed you. Go in peace’”.
This lady who only wants only to touch the hem of Christ's garment, is very much aware of her diseased condition, and acknowledges her need of a healing touch.
Everything of the spirit is contrary to what intuition would indicate to the natural man. "If I can but touch the hem of His garment" is an attitude of humility which recognizes the holiness and righteousness of Christ. Sometimes we feel so unworthy to take up His precious time, however the LORD told us we can come boldly to the throne of grace with our needs. Therefore I usually include a reference to the woman with the issue of blood and the hem of Jesus garment when praying for others. Jesus honors our faith, however small. He is approachable in every circumstance. Give Him a try next time you have a need!