I'd very much suggest you go the subscription route. As a general rule, if the channel has a subscription counterpart, it would not be legal to show the FTA signal. Now for those channels that are designated FTA (like many
IA5 channels) you would probably be ok.
While the commercial subscriptions are more, there is a financial reason for it, though it may be 'more fair' for larger business to pay it. it may be worth looking into if you can pay a commercial rate based on the size of your audience.
UPDATE: Also don't forget there are other commercial tv providers out there (LodgeNet for example). Try a google search of "free to guest programming". You may be able to find something reasonable.