If you want a scanner that can help repair old photos and also works with slides, I suggest you look at some Epson scanners, since they make several scanners that are very good at this. Go to their website and research the various models and features of each. I was able to buy a refurbished scanner directly from Epson that does all this and more. It is an older model now, since I bought it two years ago (Epson Perfection 3170 Photo), but certainly worth seeing what you can find there. If you find a model that you like, then you can shop various electronic stores, online as well as brick and mortar, for the best price.

My recommendation is to read a LOT of reviews, look specifically for what you want to use it for so you know it excels in that area. Get the highest DPI you can afford.

My scanner needs are routine, I have a built in flatbed scanner in my HP all in one officejet 6210xi which works great for me, I have had a couple of inexpensive visioneere models that were ok.

Be sure you read the reviews for flatbeds that handle slides! and handle them well and easily.

Here is a link that might be useful: reviews

I did spend a lot of time Googling reviews. A bit overwhelming. I have always gotten good advice from the folks here and thought I'd ask.

I have an Epson V200 scanner. It is a flatbed scanner that can also slide film and slides. I paid around $80 for it.

I bought this over a year ago. I am not sure of the availabilty of this certain model, as it has been discontinued, - other than eBay or Amazon.

I can scan up to 4 slides at once. You load the slide tray and press scan. It puts each slide into a seperate file. You can specify where you want them saved. It is quite simple to use and I have been extremely happy with the results.

It will scan at up to 4800 dpi. I generally scan my slides at a resolution of 600 dpi - and can get fantasic 4x6 prints. If you were looking to make poster size prints, you would want to up your dpi. The higher the dpi - the larger the file and the longer it takes to scan. If you do not have a lot of "horsepower" in your computer, scanning at really high dpi will take a long time.

Scanning dpi and printing dpi are two entirely different things. You can google and research this further if you want.

This is a slide from the early 1950's, scanned at 600 dpi.

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You can correct dust, backlighting, etc.

I think HP has a flatbed scanner that can scan 16 slides at a time..this would be sweet if you are looking at a large number of slides.

I love my Epson scanner - but have also been happy with HP scanners.

I have attached a link to HP. It is very informative regarding slide scanning.

Here is a link that might be useful: Slide scanning - from HP

Most people will not necessarily have the same usage you want. Especially the slides and specific photo needs you want, what might be a good idea is to visit some local photography specific stores in your area and talk to the people there about scanners, this would be a better place to shop than going to say like bestbuy where they just cover the basics that run of the mill every scanner will do.
I especially like the review sites that are also photography specific, likes Steves he has super reviews and recommendations. Being sure to focus on the slide aspect because some scanners do a minimal job with slides.
Epson does make very good scanners for these type needs.
This site gives some good info
film scanners

Here is the link to Steve's site he has forums there also

Here is a link that might be useful: Steve's

Continuing what Iowagirl wrote about DPI I suggest that especially any damaged or marked photos that you intend to repair be scanned at a much higher number. This gives you a high quality image that can be blown using your photo editing software thus making repairs so much easier. Afterwards if you wish these can be saved in a lower DPI