DISCLAIMER: The below is a reality-driven work of fiction

How much would it cost to buy aggressive inline skating?

Yes, all of it. Every single active company and brand.

Let's look at Rollerblade's estimated 2008 operating revenue: $20M US. 2008 was a rocky year in finance and a long time ago, but aggressive rollerblading has gone downhill in participation terms since then, so this seems like a fair starting point.

Extrapolate from this that aggressive sales represent no more than 15% of total income, but probably closer to 8% or $1.6M. Rollerblade have the best recognition and likely the best distribution of any skate brand- except for maybe K2, both due to their ski parents' retail sales channels. K2 does not emphasize its "aggressive" subcategory offering, which hasn't changed in 10 years, but we'll assume their numbers are similar or much better.
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5m

Seba has one aggressive skate and limited distribution relative to Rollerblade and K2; but a lot of folks bought them, so let's say they sell nearly two-thirds of one of the two: so 1M US gross, or about 4-5000 pairs of CJs.
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1m

Next, let's look at the equipment companies that focus on "aggressive". We're tinkling in the breeze with everything from here on out though, since there aren't any numbers available at all- but we can use the above figure along with scale of distribution to make some educated guesses.

It's fair to assume that all of the below move more product than Seba, so let's say that on average each does about 1.5X Seba equals 1.5M US. This would be 10 to 15000 pairs of skates each, which seems optimistic- but believable, given the related accessory brands, which provide some padding.

Valo (Roces)
Conference by Powerslide GmbH (USD, Xsjado, Kizer, Undercover, Street)
Razors (Razors, Jug, Ground Control)
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5m

Smaller manufacturers. I'd put each of these at anywhere from ten to twenty-five percent of the above estimate, so roughly 300k US annual gross, or around 2500-3000 pairs of skates.

Shima Skate Manufacturing
Remz
Adapt
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1m

Yes, Corr (not to be confused with Kore), Anarchy, Airwalk, etc. We're not buying the "real" companies: we're buying them all, dammit! Let's just say they do about twice the volume of the "small" manufacturers at sporting good and department stores, but for half the retail.

Corr
Anarchy, etc.
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1m

Create Originals
Bake
Youth/Themgoods
Kaltik
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200k

With a product cost of around $35 and average revenues of 25k US, each would sell 700-800 pairs of frames on average. This is probably optimistic, but seems reasonable. Let's double it for good measure.

Sic
Eulogy
Haunted
Circolo
Gawds
Scribe
Shredweiser
Dirtbox
Dead
BHC
Amall
Moonshine
Grey Matter
2-3 Others
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200k

Let's just say that on average, each wheel company does about 10k per year, or $12 per 4-pack to dealers = 800+ sets. Some do a lot more, while others do less. We'll round up generously.

Finally, consider "softgoods". Like wheel companies, there are a couple established players and a rotating cast of basement T-shirt screeners. This is probably somewhat comparable to wheel manufacturing.
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200k

Since almost all of these numbers are completely speculative, let's be optimistic and round up generously to say that the aggressive inline skating industry grosses $15M US in 2015 with annually declining revenues of roughly 5% between 2008 and 2014. Pushed to the limit, a fair market offer for all of the companies might be around $35M US, or barter for one Scarface mansion.

Of course this is purely fictional without real numbers.