Where have you seen Arapaima gigas on sale!! These are a endangered species and there exportation/importation is highly restricted if not illegal.
You also missed out the Australian arowanas Scleropages jardini and Scleropages leichardtii which come in somewhere between silvers and Asians, small jardinis start at £40 to £50 with adults going for anywhere up to £500 depending on the colouring. S.leichardtii is on the endangered list and its export/import is highly restricted so when seen the prices reflect this.