that's a sucker bet...

If you are interested in continuing with your plan, do this first. check out the ngc pop report for each quarter. take the ration of 70s to 69s, and that will give you the minimum number you will need to submit to have decent odds of getting a 70. HOWEVER, realize that most dealers stipulate when they send stuff in that anything under a 68 or 69 is to be left ungraded. (thus, your proportion of 70s to total quarters is probably much lower). As the earlier writer suggested, hit eBay or check out the adds in coin world.