I will oversimplify this (and I work like this when I have to pick a service (anything from SaaS to hiring one of them Big4+2 for a project): I want jeans. I look around. I buy jeans. I am willing to pay full price for jeans. I give proper project reqs/scope of work up front. If they fuck up, I fuck them usiny with the SLA/OLA. I also shit on them to anyone who ever brings them back (with real and damning info). If they do a good/great/their job, I "marry" them until the end of time.
If these guys "appreciate" you what you are, go for it. If they make you jump through 100 hoops then a) tht already picked option Z and they want the rest of you to voluntarily drop out of the race either through pricing (keep adding reqs and keeping the price fixed), or through features (keep adding reqs that they KNOW/sense you cannot deliver e.g. 'oh your app doesn't do liquids? too bad we wanted espresso to go with it).
Either way.. (and judging by the numbers you provided): - from scratch 60k - enhance 13k-38k
Even at the lower end (13k) it is still (almost) 25% of the whole thing..
Doesn't look like a good deal for you.