I recently made this exact same switch with Comcast. I'm also experimenting with alternatives.
The first experiment I'm trying is FreedomPop. I've ordered the ~$30 wifi hub which comes with their FREE 500MB/mo account. Their plans break down like this.
Free - $0.00/mo
Data Limit: 500 MB
Additional Data: $0.02/MB ($10/GB)
Basic 1GB - $9.99/mo
Data Limit: 1 GB
Additional Data: $0.01/MB ($10/GB)
Casual 2GB - $17.99/mo
Data Limit: 2 GB
Additional Data: $0.01/MB ($10/GB)
Premiere 4GB - $28.99/mo
Data Limit: 4 GB
Additional Data: $0.01/MB ($10/GB)
Premiere 5GB - $34.99/mo
Data Limit: 5 GB
Additional Data: $0.01/MB ($10/GB)
Premiere 10GB - $59.99/mo
Data Limit: 10 GB
Additional Data: $0.01/MB ($10/GB)
The quality of service depends on the wifi hub you purchase (3G, or 3G/4G) and your location on their coverage map.
http://www.freedompop.com/coverageOne catch is that basic plan quotas do not roll-over month to month. Depending on your actual usage,
We now offer an additional FreedomPop Data Rollover service for $3.99/month that will allow you to rollover unused data up to 500MBs per month for up to 20GBs total. You will be able to share your rollover data with friends, and roll over any unused 500MBs on any plan.
If you do not enroll in this service for $3.99/mo, your full monthly allotment of data you will start over at the start of the next month.
So depending on your usage, for $3.99/mo you could have more than 500MB on your plan. I'm not sure how all of this works out in reality, but I'm about to find out. 8)