combotrader
Their are 3 options as far as TradeStation is concerned,
1. Buy a copy of the TradeStation software and subscribe to a 3rd party data vendor.
2. Subscribe to Tradestaion for the platform & data feeds you require. Off the top of my head they charge about $300/month plus your exchange fees.
3. Open and fund a brokerage account with TradeStation and get the platform fee (including RadarScreen) waived if you make the transaction volume specified on the URL i provided earlier. Alternatively if you fall short of the monthly requirement it will cost $99 for the platform fee (including RadarScreen).
Regards
TMM
P.S. No complaints with the TradeStation brokerage service.