Lord knows I've made enough posts on this topic on the official forum:
There's a reason you need 10 heroes. For argument's sake, lets say you only need five. Unless your five are Murky, Abathur, Azmodan, Sonya and Chen, odds are some if not all of your heroes are going to get picked. What then? The game assigns you a random hero that you've potentially never played before? Or say you have a hero left to choose, but it's a nonviable pick in regards to the team comp (say, a third warrior).
Funny enough, ALL of the 2k gold heroes are good picks in Hero League and some that are 10k are pretty much garbage. Not perfect, but good. Muradin is a top tier tank and ETC is pushing top as well, Valla is the best ranged Assassin in the game, Lili is a not too shabby healer as is Malf, Raynor is solid. Do you know how long it takes to make 2k gold? At worst a week's worth of daily quests (assuming you get nothing but 200g quests). Factor in the amount of time it takes to get up to level 30 to even play Hero League and you should easily have enough gold for at worst half of the necessary heroes.
Do yourself a HUGE favor and get each week's free-to-play rotation of heroes up to level 5. Each one at level 5 is 500 gold. Factor in the 30 something heroes in the game and that's a crazy amount of gold to be had. It might suck playing heroes you have no interest in owning or learn to hate (I've lost every game I've ever played as Kerrigan), but it's also a great way to learn your advantageous encounters and your disadvantageous encounters.
And if you're not totally adverse to spending money, keep an eye on the weekly sales for good deals on heroes. Stitches is the most broken piece of shit in the game and is only $4 this week. If you want a steal, get the bundle that's $5 for Muradin, Malfurion, Raynor and an Armored Horse mount.
NOTHING forces you to spend money on the game to get into Hero League. Be glad that Blizzard isn't listening to the people who want you to have 15+ characters in the event of bans or that you've got to have however many heroes at no lower than level 8 before even wading into Hero League.
Not quite sure why the prices are what they are, but for the time being, that is a choice that you'll have to live with.