You've not stated what film format your slides and negatives are in. If it's 35mm, you can scan them fairly easily using something like this:
http://www.jessops.com/Store/s49760/0/Scanners /Veho/35mm-Film-Scanner/details.aspx?&IsSearch =y&pageindex=1&comp=y
For less money, you could buy a decent combined flat-bed and film scanner such as this one from Canon:
http://www.jessops.com/Store/s36229/0/Scanners /Canon/4400F-Flatbed-%2b-Film-Scanner/details. aspx?&IsSearch=y&pageindex=1&comp=y
(I use the immediate predecessor to that model, the Canon 4200F and can vouch for the quality). However, it's 'fiddlier' using a combined scanner than a dedicated film scanner.
Unfortunately, if your slides and negatives are in a non-35mm format (such as on 120 or 127 film), there are no reasonably priced scanners available. This question has arisen before and there seems to be nothing available except for 'professional' film scanners, with a price tag of over �1000.
Chris