In no particular order, Iceland, Norway and Switzerland are probably some of the most expensive countries in Europe to visit, so always something to be mindful of.
When you say £500-1000 what does this need to cover? Just flights and hotel, or all spending money?
I would look at a small apartment, so you can buy some food/drinks from supermarkets to reduce the cost. When I'm alone, I prefer eating out at lunchtime, I like to eat more then anyway, rather than in the evening. Then you could just have easy food in the evening in the apartment.
Poland is very affordable and one of my new favourite places to visit. Cities such as Gdansk and Wroklaw are beautiful (not been to Krakow) and often have cheap flights from the UK. Eating out and accommodation are good value, good public transport. You could fly to Gdansk and spend some time in the city and also at the nearby coast, which is very wellness and nature focussed. I went to Gdansk but also picked up a leaflet about Sopot which is on the coast and not far by train. There's also forest walks just inland.
For best priced flights, look at skyscanner to see where you can fly to from Glasgow and go from there - can you also fly from Prestwick?
3 hours from Glasgow will get you as far as northern Spain, Poland and Germany. Perhaps northern Portugal. If you're happy to fly a bit further, Lisbon and southern Spain will be in reach. There's always loads of well priced UK flights to Malaga, which as well as being a lovely city, has a huge botanical garden that's just on the northern edge of the city and easily accessible mountains inland by train or coach. You could also go to nearer Spanish cities like Alicante, Girona or Barcelona.