Well, I am sure both are expensive to maintain, probably need more maintenance and inspection. But with the ties with India, I don't think spares are a problem. Yeah, Eastern parts are probably cheaper than Western parts. Also don't forget that the Flanker's engines come from a very capable and experienced engine company.
The AL-31F design was actually based on the RD-33. Now, I don't have many numbers, but my Flanker book tells me the AL-31F has an original life of 1,000 hours and specified life of 1,500 hours (not sure what is meant by that). It also says they are superior to the F100 and F110 engines, including longer service life. Regarding the AL-31FP TVC engines... I'd say more moving parts, more maintenance.
The MiG-29 fullfilled the low in the high-low fighter mix, I'd be surprised if the MiG-29 maintenance-wise would cost more than a Su-27, it's only a slightly older design. The Su-27 was designed to beat the F-15, not to be more economical to operate.
Maybe you can find info regarding MiG-29 maintenance from German sources, to compare with western aircraft. For Flanker vs Fulcrum info, I guess it depends on what is released from India. Maybe there is info from Russia, but I haven't got it.