I take it as what fits in your budget. Sometimes, I'll end up with an unexpected need (like a new enrollment, when I had a home daycare.) I haven't budgeted for it, so yep, I have a Scenera I use. I was able to squeak it in when the budget was $0. On the other hand, I knew dcb was likely to hit 40lbs before 3, and I wanted a Radian for him... I was able to afford it, if I skipped some things on the personal end. I decided it was worth it to me, and I made it happen.
If you have six months, then I would decide what you want/need and set aside a bit at a time. A Scenera, for example, fits a newbie, can ERF to some degree (I have one who outgrew it at 20mos, and one who still fits at 4y3m,) and will last for several years overall. If you want a RN, then you'll need to sit aside 4-5x as much every month. If you can't do that, then the Scenera is a fine seat.
I'm struggling now with whether I can "afford" a Monterey. I have several boosters my boys (8.5 and almost 9) can use, but they're either NBB or the backs won't support them when they sleep. (The 8.5yo falls out of the Pronto.) So do I "need" the seat? Maybe, I think so. I can afford it, but only if I pull the cash out of my fledgling emergency fund.
If I had to put it on credit, or other things were going to have to sacrifice in order to get it, I would get the least expensive seat possible to fit my needs at the moment. That's all I can afford. I have BTDT and it's part of how I ended up with kids in Sceneras, Cosco HBBs and NBBs by the time they were 3. If I had it to do again, I'd find a way to do better, but I did the best I could at the time.