If all you want to do is cover the fence, maybe something like Ivy (although this can be a bit of a thug, so be sure this is what you want). Another climber like honeysuckle or jasmine, or even a clematis would be nice - you need to be careful with honeysuckle as it will form berries that look tasty but are poisonous.
Like Matty says, you need to dig lots of goodness back into the border, well rotted manure, compost, spent compost from hanging baskets etc, as conifers do suck all the goodness out of the soil.
Places like the pound shop, Aldi, Lidl, poundstretcher are really good for cheap plants and equipment, sometimes you need to be there on the day things are delivered to ensure you get what you want (and that it's in decent condition). I find that the shopping channels can be expensive. The co-op was doing bedding plants last week, 2.50 for a tray of six, buy one get one free (so 12 plants for 2.50), sweet peas, marigolds, sweet william, snapdragons (and something else I can't remember - pansies maybe).
You could concentrate on getting the soil right this year, and buy some dwarf fruit trees in the autumn or next spring, it's a bit late to get them now (in spring Aldi was selling fruit trees for 3.99 each, a fraction of what they cost from the garden centre or by post. I also subscribe to the suttons and t & m e-mails, as sometimes they have offers on that would be rude to refuse - just rembember to add another £5 for p&p!
Keep an eye out at your local supermarket, sometimes they have offers on too. You will soon learn where to look for bargains! I only use the garden centre if there's something specific I want. Blooming direct is also brilliant for decent sized bedding plants, and you can choose the week you want them delivered.