Price guides can be a helpful, but it's important to understand exactly how they work. You might also search completed eBay auctions for similar collectibles and compare what you're willing to bid against what others have previously paid. When you decide what to bid, bid the maximum amount you would pay for the item. You'll remain the high bidder until the bid amount reaches your limit. Regardless of how much you bid, you will receive notification by email if someone outbids you.
Many bidders feel the notification alone makes it worthwhile to bid early.
It helps remind you of items that interest you and keeps you checking the auction. A trip to the library or bookstore is worthwhile too. You'll get a better idea of what to look for and which questions to ask. If you're happy with the seller and the transaction, do more than leave positive feedback. Tell the seller what you collect, and what you hope to find in the future.