You can still take some financial short-cuts. For example, instead of sinking the money into command blisters, consider taking some regular troops that have a cool pose and mount them up on a rock or other small terrain feature so that they stand out from the rest of the force and say he's a Captain. Similarly, take a model that has a spear held high, cut some paper or card to shape, glue it to the shaft and you have a Banner. Now you just took two plastic models and made a $20 command blister.
You may find other options like this as you go along, and never get too hung up on having "use as" models in your force as long as you and your opponents are clear what they are. For example, if you're playing Evil and want to try some Nazgul, pick up one you think you may want. But over the course of games if you want him to be the Dark Marshal in this game, and Khamul in the next, just be sure you're clear before the game starts. There's no reason to worry about having to rush out and dump money again.
Also, look around for non-GW options while you're getting started. I wanted some Eagles to support my Wood Elf army but don't have the money to spend on the GW models right now. A quick trip to a toy store though found some plastic Owls with a similar wingspan which I stuck to the right size base using Blue-Tac. For $5 and about 30 seconds of effort I had two "Eagles" ready for play. I also own a few Trolls, but don't have an offical Troll Chief. I can always just say my Isengard Troll is a Troll Chief and my others are normal Mordor Trolls and me and my opponents are very clear and have no problems.
Also, if at all possible, try to borrow a friends army for a few games. Make sure you like how it plays and it meets your style before starting to invest. When you're just getting going you don't want to commit much of your cash to one army only to find you really wished you did something else once you really get a feel for the rules and play style.
Welcome to the obsession!