Cost may be due to several factors. For example,
Round 2 is based in the US (Indiana), Bandai is headquartered in Japan (Tokyo), and Revell in Germany (Bünde). Generally, injection molding production costs in the US are extraordinarily high compared to production costs in Asia or Eastern Europe. Many plastic kit producers will outsource some or all of their actual production to lower-cost locations such as Poland, China, India and the Philippines. The initial designs and packaging are usually made in the "home office". But actual production is moved elsewhere. Those who do move production to lower-cost locations may be able to sell at more competitive prices.
In some cases, as a cost-saving measure, some model companies in the West contract steel mold production from another company, say one in China, and as part of that contract, a set number of kits are produced from the mold. Although the model company may retain copyright of models produced from the mold, the model company doesn't actually own the physical steel mold. The contractor might, depending on the terms of the contract.
Most of the US-based injection-molded plastic model kit companies we grew up with have gone out of business or suffered major financial restructuring. Round 2 often purchases steel molds from model companies no longer operating. But some of those molds are not in usable condition. In other words, they have deteriorated to the point that you can't actually make a model kit from the original steel mold.
There has been some discussion on other sites that explain that some of the "repopped" models offered by Round 2 are actually made from new steel molds designed by Round 2 from scans of the original models. Steel molds require costly care and maintenance and will deteriorate over time, especially if stored improperly. In some instances, the original molds bought by Round 2 from out-of-business companies were in such poor condition as to be unusable and unrestorable. So, talented Round 2 designers reportedly scanned vintage models made years ago from the original, now useless molds in order to create new, usable steel molds from new designs based on the scans.
Steel molds are breathtakingly expensive to produce, especially if cut in the US. So even a "repopped" vintage model actually made from a new steel mold made in the US may be produced at the same cost or even more than an entirely new design made overseas.
Some Round 2 products may be comparatively expensive, but at least Round 2 is one of the few US-based plastic kit manufacturers still operating.