This is going to be outside your bufget, but the info may help.
The car you see in my sig below, is my cabrio. It used to run 17" wheels with a 40mm drop. The arches were rolled, but this is not as expensive as you may think, and will come within your remit if you are just changing the springs. I have since changed for 14" wheels and coilovers giving an estimated drop of over 80mm. This is quite an expensive set up, but IMO looks fantastic. For practicality I would just change your springs for a 40mm set and get the arches rolled (just in case, but I cannot see it being a problem really) This can be done, if you are going to change the springs yourself, for under ?400 easily.