The Wynnstay Hotel in Machynlleth ('mackh-unthleth' is about as close as an English speaker gets) do a set meal on Wednesday market days: £10 for two courses, £12.50 for three.
Example: Soup*/Potted Welsh ham, house chutney; Carbonnade of Welsh beef, crushed potatoes, panache of veg., or courgette, sweet pepper and mozarella quiche, potato and veg.; Chocolate ice cream sandwich. a four-, bordering on five-star meal, for a three-star price.
*Carrot and coriander soup seems to be compulsory in Wales.
The hotel is old-fashioned in a good way; the staff are courteous and helpful.
Tip: served from twelve noon. Go early, the dining room gets busy.