Is there anything in the Act that requires the cost of those tools and parts to be reasonable? Yes: "on fair and reasonable terms."

Is there anything that allows third parties to manufacture aftermarket tools and parts? I don't see anything in the Act that specifies that.

Fair and reasonable terms:

(4) “Fair and reasonable terms” means each of the following, as applicable:
(A) At costs and terms that are equivalent to the most favorable costs and terms under which the manufacturer offers the part, tool, or documentation to an authorized repair provider, accounting for any discount, rebate, convenient and timely means of delivery, means of enabling fully restored and updated functionality, rights of use, or other incentive or preference the manufacturer offers to an authorized repair provider.
(B) For documentation, including any relevant updates, that the documentation is made available at no charge, except that, when the documentation is requested in physical printed form, a charge may be included for the reasonable actual costs of preparing and sending the copy.
(C) For tools, that the tools are made available by the manufacturer at no charge and without imposing impediments to access or use of the tools to diagnose, maintain, or repair and enable full functionality of the product, or in a manner that impairs the efficient and cost-effective performance of any such diagnosis, maintenance, or repair, except that, when a tool is requested in physical form, a charge may be included for the reasonable, actual costs of preparing and sending the tool.
(D) If a manufacturer does not use an authorized repair provider, “fair and reasonable terms” means at a price that reflects the actual cost to the manufacturer to prepare and deliver the part, tool, or documentation, exclusive of any research and development costs incurred.