It depends what you mean by inexpensive.
Panjea - a great Indian restaurant beside the Mitchell library Charing Cross - just great food - the chef takes a great pride in his food - I spoke with him on one of my multiple visits there earlier this year. The lamb dishes are phenomenal - I reckon two people could eat and have one drink for about 25 pounds per head.
The University Cafe on Byres Road - across from the Western Infirmary (no jokes please) - the food has been great for as long as I can remember - and be sure to ask the waitress what is cooking in the back - not everything appears on the menu. A personal fave was always mince and chips - they just did it right. Not exactly where i would try to impress a client or a date - but the food is very good, very reasonable and very unpretentious - a rarity on Byres Road.
Does anyone have a report on the new Malaysian near St George's Cross, including menu and pricing details?
Cafe Gandolfi in the Merchant City. Famous, informal place with very good food. It's been a few years, but the one thing I'll never forget is the best adult chocolate sunday ever. Very sharply ginger ice cream with a very rich, very dark chocolate sauce. Note: I am not normally a dessert lover, but something like this could make me a convert.