Any suggestions on alternative advertising solution similar to Project Wonderful?

Unless you have sites with massive traffic, it's probably not worth the hassles to manage your own ad sales. One alternative are the broker sites like BuyAds.com or BuySellAds.com

Very large sites that manage their own ad space don't usually have a bid model, rather they negotiate prices on an individual basis, based on the volume of the buy. The 'list' prices given on their advertising info pages are commonly well over-priced for the corporate buyers who have a fixed advertising budget they have to use up, more careful advertisers usually manage to negotiate something much more reasonable, 1/2 of that list price in some cases.

The down side of the Project Wonderful may be standard ad buying conversion metrics may be harder to apply, making comparison to other ad sources less direct.

When you go through Google Adsense your spots are priced by competitive bid, though if you see generic or retargeting ads popping up, chances you have 'remnant' space not getting any bids.