Electricity is a HUGE expense...not to mention the air conditioning for the amount of heat she must be giving off. She is most definitely an expense.
You can't buy love? Marigold just did, she bought her a chassis that must have been at least 20k. I don't remember Momo giving her tons of hugs and telling Marigold how much she loved her before that.
The LEAST Momo could do is work out a way to pay her back, not because she has to, but because she should. A good friend does not take a huge gift and not repay it, Momo was ready to get a job and buy it herself so she still better be willing to do the same after Marigold bit the bullet for her.
... are you seriously suggesting that Momo did not love Marigold before this? We're talking about the same AnthroPC, right? The one that has hung around in lousy living conditions, looking out for Marigold's physical and mental well-being to the best of her doll-sized ability and trying to help her to break out of her shell? It was explicitly stated in the description on page 1996 that "Purchase of an AI is not a binding contract- either party is free to terminate the relationship at any time, and the transaction agent will refund the contract fee." Momo could have left Marigold to drown in dirty laundry and pocky packaging at any point, and she didn't, despite clearly being irritated by Marigold's behavior. She was also hardly on a convenient scale for hugs, but Momo has always been fairly physically affectionate for an AnthroPC - particularly in her habit of riding on Mari's shoulder or piggyback, whereas Pintsize and Winslow mostly seem to walk if they go out in public at all. I'm not surprised she's graduated to hugs now that her arms reach all the way around.
I never said that Momo didn't intend to reimburse Marigold, I was just pointing out that she could pay her back with interest and still feel indebted.
(And I'd estimate somewhere in the range of $1K - $5K for the chassis; it may be higher end but it's still an off-the-shelf model they got at the mall.)
Taking the topic to a different vein, I think it's kind of interesting how Momo has become so much more of a "main character" than the other AnthroPC's. Almost every comic featuring Marigold has featured Momo, and in all of them Momo has acted much more human than Winslow or Pintsize have towards their respective owners. It's much easier (for me, at least) to forget that Momo is actually an AnthroPC and just think that she's a tiny human.
I think it's partly the differences in the dynamics between the different AnthroPCs and their owners - in a lot of ways, Marigold has needed Momo to be more human than, say, Marten has needed Pintsize to be or Hannelore has needed Winslow to be. Marten regards Pintsize more as a pet than as a friend or companion (which seems to suit Pintsize just fine, in part because of the utter lack of accountability their relationship places on the AnthroPC. Hanners depends a little more on Winslow for friendship, but at the same time, being around people is not always enjoyable or restful for Hanners and the last thing she needs is another human running around her apartment, even a tiny robo-human. But Marigold craves human contact without being quite sure how to go about getting it, and it's strongly implied that before she crossed paths with the rest of the cast, Momo
was Marigold's social life.