At my local U-Pull it I think the gauge was only $5 bucks but then I had to go back for a whole cluster which I think they charged me $20 for a complete cluster. I transfered my speedo, fuel gage and temp gage because I wanted to keep my mileage and all those gauges were working just fine. I now have spares just in case. Make sure the dash matches. I have an 89 and the later dashes are slightly different. In your case make sure you do not get an early version. By pulling it yourself you can get practice on a junk yard car before working on yours. I would not worry too much about the used gauges they are protected pretty well in the dash and rarely go bad. Find the lowest mileage car to pull it from for a little extra insurance. You could just get a complete cluster from the junkyard and have a complete set of spare gauges.

 

I like to search ebay with terms like S10 NOS or Blazer NOS. NOS is new old stock and sometimes you can find Old but still New OEM items at a fair price. I purchased my sid mirrors this way. GM Factory Mirrors at a fair price. I had a pair of mirrors that I got from LMC and the quality was junk to put it bluntly.