Needless to say, what you have to spend depends in great part on what you already know, what you want to find out, and where you have to look for it.
For a Fagan woman immigrant to America from Ireland, at the time of the Great Famine, I found her parents, three of her four grandparents (though without a maiden name for her grandmother), and the towns where they lived in America and Ireland.I identified siblings in her and her parents' generations and traced their descendants to 1930, and in the case of the woman's brother to 1965.
The search has extended over about 6 years supported by subscriptions to Genealogy.com and Ancestry.com for some of those years.Several trips to the American home towns and the Irish home town were made, but some of the Irish info could probably have been gotten just as well by mail.Not so the American, and I live about 1700 miles from where I had to go.As a rough guess, I spent about $200-$300 to purchase copies of documents and to bring in microfilms from distant libraries, and about 90 euros on searches in an Irish county heritage centre.
You can get the current price of subscriptions to Genealogy.com and Ancestry.com from their websites if they are relevant to your search.The price of travel varies, of course, with where and when you go and how much comfort you desire or require while away from home.
I could give more details if you want them.Also, I might be able to make my comments more pertinent if I knew somethingmore specific about your known ancestors.You can email me if you wish.