Most of the metal parts; frame, shifters wheels, etc. should be good to go with a good cleaning and re-lubrication or greasing. Even a frozen stiff chain can be rehabilitated by a spending a couple day’s soak in ATF.

You already know that you’re going to have to replace all the ‘soft’ parts just to make it rideable. At minimum, you’re looking at $75-$100 fwiw.

Depending on where and how you shop:

$40-50 for tires
$10 for tubes
$5-$10 brake pads
$5-15 for bar tape
$10-$15 saddle

You’ll really have to scout the clearance rack and not be too picky to get the best prices.
If your LBS has a take-off bin, you can get a decent saddle for almost nothing.

New cables and chains are nice, too, especially if the old ones aren’t working, but it’ll push the cost up a little more:
There’s a $10 Bell-branded cable kit at WMart, that’s good for older bikes like this.
The KMC Z51 chain is my go-to for ‘ten-speed’ era bikes. I got a couple of them from my co-op for $8 each