STI shifters (also known as brifters) are expensive. Even 10 year old models tend to go above $80 on ebay.

Upgrading an old road bike to STI shifters is certainly possible, but it tends to be a little costly, as in $150 or more for all the necessary parts.

If you don't like downtube shifters and would prefer indexed shifters, but are willing to go with non-integrated shifters that would be installed on the flat part of the drop handlebars, consider the $15 Shimano SL-A050 shifters - 7 speed indexed, would allow for an affordable conversion of an old road bike - but they're not brifters, they're still separate from the brake levers.