We have a Next 2 Me and really like it. DD is 7 months and still fits in, so it's got much more use than the Moses basket did first time round (DS was out of it at 4 months or so, plus it was really creaky when he was put in and that used to wake him up!).
We didn't replace the mattress because it came from SIL so we know it was clean - just gave it a good wash and aired it. The mattress has a cover that comes off for washing, leaving just a foam bit inside that can't be washed. If I hadn't known where it had been, I'd have got a new mattress.
Bear in mind, if you buy it, you can always sell it on when you're done, so factor that in when you decide whether it's worth it.
I have a next 2 me and it was the best thing we bought for dd! They are expensive new but the mattress can be taken out so assuming you can just replace That? Dd is 3mo and very long and still fits in it with plenty of room. She hasn't been able to go in her Moses basket downstairs since she was 4 weeks old!
I ended up doing the same calculations you've done - second hand crib plus new mattress wouldn't save much money. So I decided to go for new, partly on the basis that I should be able to sell it on for a reasonable amount! I found an online deal which came with three free sheets, which helped a little!
U can buy the mattress for them on eBay/Amazon for a lot less than £40 but it’s not the Chicco brand however states it will fit.
I have a next 2me which bought for my 3rd son, he used it until he was 1yr old about, it was great! I wish I had bought it sooner! Using it for next baby which is due in November, and have replaced mattress. Bought it new, everyone feels different if u can afford new I would get new x
I'd read safety guidelines on baby beds and all have clearly stated to buy a brand new mattress for a new baby, regardless of who had it before or for how long. Not sure why - avoiding the mattress memory of a baby's shape as that can allow a rolling baby to get stuck face down, maybe. But I'd get a new mattress just in case.
I bought a second hand next to me for £65 and the mattress for £20 on amazon which fits perfectly. I washed it five times and it's like new. I've also bought a pack of two fitted sheets for it on Amazon at £12, better than the £20 chicco price.
If you don't care about the next2me bit, have a look at the chicco lullago - it's a travel cot with a crib and a cot height. We used it in our room on the crib height in between the Moses basket stage and moving DS into his own room, and now it's our travel cot. Still expensive but at least we'll get 18months+ usage out of it rather than 6!
The reason they say to replace the mattress is because mould can easily grow inside them from sweat/sick/milk/whatever it's too reduce the risk of SIDS so personally would buy a new mattress every time for every baby even if I'd brought it from New xxx