You willa ctually find very few restaurants in San Miguel at the top end mentioned above. I have nver spent $100 US for two, although I know there are a few places that could happen. Most nice restaurant meals will tend to run about $20 per person (or less) not counting wine. The decent place I eat in--like Rincon de Don Tomas, Ten Ten Pie, Buen Cafe, I seldomj spend more than $12-14 for a nice meal. I also eat at places like the "No Name" restaurant on salida a Celaya (next to the TelMex office) where a full comida with a fruit drink is $40 pesos (less than $4 US). Last week two friends and I had a taco dinner at Don Felix in Independencia and the bill for three was under $130 pesos.
One of the nicest new "gourmet" restaurants in town is "The Restaurant" on Sollano. A very talented and creative young chef. If you drink a lot of wine, you could spend $50-60 or so per person, but you can also eat there for less.
Other good bets: CasaBlanca, Tio Lucas, La Brasserie (which is Cafe de la Parroquia by day), Romanos.
If you're looking for the least expensive places in town, do check out Carol and Norma's site, the Cheap Eats page.