The amount of people that purchase these type of ovens is small so the guys that import them feel obligated to overcharge you because they can. They wouldn't even import the things if they only made a measly profit. One tip is to try kitchen stores, the ones that sell kitchen cabinets, the ones with domestic cabinets would be cheaper. They sell wall ovens that are Taiwan made and look just like their foreign counterparts, probably because a lot of gas ovens are made in Taiwan and that is why there is an import tax(import tax not that high) to protect their domestic manufacturers. The thing is no one buys these so they are not really protecting any kind of market. Anyway. the shop I went to had wall ovens for only NT$20,000 but they were small. They looked nice, stainless steel, but the inside was small. Maybe the same size as my Japanese/Taiwanese style high-end counter top oven, which also NT$20,000.
There is also a Kenmore dealer on the corner of DeXing Rd and Zhongcheng Rd in Tianmu, on the NW corner. They were fairly reasonable.
Buying from departing expats might work, if I see any on the board at the American Club I will let you know.
By the way, if you do buy an oven, you can make money with it, selling bread and cookies and cakes to Taiwanese, ahahaha...they just love baked goods, but they only have a WOK at hom eand wouldn't know how to bake bread or cookies anyway. Just look at the lines at the bakeries and scratch your head and wonder why more people don't bake their own stuff at home? Anyway, that is just a joke, please don't sell bread on the streets and lose your shirt, because if you can't make rousung, yumi or hongdou minabao, you won't make any money, unless your last name is Wendel, just stick to teaching English.