No need for 2 routers. Here's what I would do, until I knew better...
1) using a 29.95 router (ie assuming one-size-fits-all port controls) connect both computers and the modem to the router. But plz remember the guideline (not edict), spend more, get more config options. You may WANT or worse, NEED them in the future.
2) On the trading machine use port-blocker software (not a firewall, but similar, and much much lighter!) for the unwanted ports. The router will likely allow your trading apps access with no adjust needed. Byproduct of using a port-blocker on the trading machine is you can make changes easily (for software updates, different warez, etc) without affecting anything, including the router, other than this computer.
3) On your surfing machine, use
Shields Up to assist configuring the router for "stealth" operation (ie ports). There are other similar services, but this one has been around a long time and is certainly a good starting point. Then retest your trading computer to make sure all your trading apps still operate.
As for a port-blocker. I recommend a freebie
Emsa Port Blocker There are many others though. I like Emsa because it lets you specify remote(outgoing) and local(incoming) ports to block. Some others only block one or the other. For your needs, you might block remote port 80 (http), now you can't even get there, and local port 80 incase some rogue app decides it wants to accept http connections. Obviously, the router needs port 80 open if you plan to do any surfing on the other machine.
Again, HTH
Osorico
EDIT: almost forgot, Emsa is free but requires an activate code. It's a bit confusing, imo. Just read carefully. No personal info is asked for or needed. Kinda silly.