You can get the Dishstore rebate without a contract, but its only going to be $25.
Do the math here for what you DON'T get when you sign a contract...
#1 Pay a $99 activation Fee
#2 $120 in credits for Turbo HD Bronze ($20/mo for 6 months)
#3 $25 in additional Dishstore Credits.
Right there you have, your missing out on $244 in credits. Cancellation fee with Dish is only pro-rated at $300, which is $12.50 for every month remaining in the contract.
If you kept the service for atleast 6 months, cancellation fee would be $225, at which point you got more credits back because you took the contract.