It all depends on how deep your pockets are and how much you want do as far as marketing, selling and the size of inventory you can handle (land and money).
Anybody can easily get into the large block market, because of the low investment and technology BUT the market is much smaller and expanding it calls for marketing and sales (not selling or price). You can just buy some forms, but your capacity will be limited by the number of forms. You can always forget about a batch plant, aggregate, mixer, etc. and just buy the concrete from a ready-mix company cheaper than you can make it. The down side is that the ready-mix companies can get into the same business cheaply and compete with you.
Trying to develop a market for whatever large unit you choose, will take time and money and not just a cheap unit price. Depending on the area the other types of retaining wall systems may be established in the market with dealers and acceptable approvals. The existing markets require diversified products and applications.
If you are interested in the smaller SRW units (under 80#), you are looking at a big investment. You can buy an old concrete block plant (if available) for about $2,000,000 that can also make other products. The alternate is to buy the equipment for a new block operation for about $3,000,000 to $5,000,000 and then get the land and zoning.
As far as the major 4 SRW brands (Allan, Anchor, Keystone and Versalok), generally they do not manufacture blocks, but have developed the products, tested, written ASTM specs, matketed their systems, trained manufacturers and supported users, and contractors when needed both internationally and domestically. Check on the availability of the possibility of getting an exclusive manufacturing area license for your area (usually about 50-100 mile radius). The license precludes making competitive products. Most of the major metro areas are taken but adjacent areas are available and freight cost is less per sf for these type of products than other types (large). You can always come up with a "knock-off" similar product and face the eventual law suits because the domestic and international patents are very tight.
Regarding you last question, price of the product itself is not factor because the decision on an appearance is made befor buying. The wall heights are also not a major factor since the SRWs have been built on engineered projects that were 45' high.