In Malaga, the street called Calle Marqúes de Larios and the surrounding area is where all the Spanish fashion shops are found, but because it's Semana Santa some of the shops will be closed and street will be closed off for the processions. Holy Week is a fab time to be in Malaga, it's going to be very busy, but IMO it would be ‘criminal' to be so near and not go and see some of the processions.
I think SMa has just about covered everything.
Spanish ‘quality' labelled clothes are not cheap and imo Corte Inglés is not necessarily a place that the Spanish guests would flock to for a wedding outfit, (OK for you because you're not attending a Spanish wedding) because they too would be mortified to arrive in the same outfit as another guest, and some of these weddings have over a hundred guests, so it would be near impossible to find out what everyone was intending wearing, therefore they do tend to pick the material and have it made with their own stamp on it, or they go to special shops in Malaga where the outfits are 'one of a kind' and they pay an awful lot of money for them, but with their extended family structure, there's a good chance that they will use them more than once in a year or maybe two years. They always amazed me because whatever shape or size they may be, they have this knack of looking elegant and slightly understated, so that they never ‘outdo' the bride.
The last time I was in El Cortes Ingles in Malaga was a few years ago hunting for some books for my Spanish teacher and I don't think the items are cheap (just my opinion) I think maybe it's just the convenience of being able to find everything you want under one roof, rather than going traipsing around the city and whilst some Spaniards love it, especially if there was no opportunity to buy certain items without travelling all over the place before the Corte Inglés store was built, there are some Spaniards who don't like the store because it's growth has put plenty of local traders out of business. I suppose just like a Tesco store can do to your local high street....swings and roundabouts, horses for courses!
Without knowing your budget and how formal/informal you want to be, it's difficult to give any more advice.
You say you don't want to pay ‘mother of the bride prices, well personally I think you'll have a shock when you see some of the prices in Spain for good quality clothes.
There's a shop in La Carihuela in Calle Bulto on the right hand side as you are walking up from the hotel Cabello and it's near the top of the street, and they stock some lovely clothes and evening type dresses ( depending on the season) from names like Pomodoro and Soreto"¦"¦from the outside it looks like any other tat shop with a rack outside of reduced tops and skirts , but inside they have some gorgeous dresses, so depending what your budget is and how formal/informal you want to look, it may be worth having a peek inside"¦..you never know.!
Last year I bought a Pomodoro dress which is mid-calf on me and it's made of chiffon type floaty material with white, coral, brown and black colours, and I paid 20 euros for it, reduced from 100 euros because it was September and the winter stock was being put out on display, and the same dress despite being last season is still being offered for sale for £60 on the internet today.
I teamed it up with a black fine wool knit bolero type jacket and wore it when we went out for a meal during Xmas, but I could quite easily wear it for my son's wedding with a nice hat and a thinner and brighter coloured bolero top or jacket.
If you can't face the thought of how busy the city of Malaga will be during Holy Week, there's also Fuengirola to visit because around the main square (Plaza de la Constitucion), there are some designer clothes shops and small boutiques, and a smaller Corte Inglés store which I believe (I haven't been) is at the Los Boliches end of the resort and the Mirarmar shopping complex in the opposite direction at the castle end of the resort.
Sanji