Yes. F9 has a catalog payload to mars of 4020 kg [1] and Spirit and Opportunity had a total mass of 1,063 kg [2] each. So an F9 launch could easily launch 3 similar missions on a single rocket (the MERs were launched separately on Delta II rockets). Squeeze out some weight (material advances, fuel optimisations, better transfer windows, etc) and you could probably get 4.

Anyway, in a CLPS type program you could also cover kickstage development, like some of the new companies are proposing. Impulse Space is working in that area, developing intermediary stages that can take payloads from LEO to GEO, TLI and TMI.

[1] - https://www.spacex.com/assets/media/Capabilities&Services.pd...

[2] - https://en.wikipedia.org/wiki/Mars_Exploration_Rover

A Falcon Heavy launch is about 30% more expensive than a Falcon 9 launch, given the reusable mode. I suppose it's the servicing the launch that costs most, not the fuel or insurance premia.