An original white PCE is usually around $80-100 I'd say, but a cheaper option would be to get a PC Engine Core Grafx (Or Core Grafx II), which practically looks the same, except it's black with blue text that says "CORE GRAFX" and it has AV ports and those go for around $50-80.
I'm not entirely sure how to mod a region switch yourself, but if you check or post in the mod forums you'll probably find a lot of information. Modding it yourself cost about $20 in parts if I recall or you can send it to someone to get mod, which can be around $60.
I know most of the options aren't really cheap, but converters themselves can easily go over $100 and there are only one or two of them that are really reliable and even those have problems I think.