Panasonic ebay outlet sells refurbished ones with 12 months warranty now and again at £79.99. Last one was in December
Panasonic DP-UB420EBK SMART 4K Ultra HD Blu-ray DVD Player Twin HDMI WiFi | eBay
Although they don't ship to Ireland but if you know anyone in the UK who could get it sent to them and then ship it to you wouldn't be that big of a problem.
They also do refurbished UB820 for £220 now and again. Last one was 22nd January
Panasonic DP-UB820EBK 4K Ultra HD Blu-ray Player - Black for sale online | eBay
Same Ireland delivery exclusion.
For a C6 I'd say go with a Sony X700 as I don't rate the 2016 Oleds for their HDR10 processing (their DV is better if my E6 is anything to go by) and the X700 allows 'forced' DV playback for HDR10 UHDs. This forced DV works in effect as similar to Optimiser as regards to high nit UHDs in that it reduces clipped highlights. See post #726
Sony UBP-X700 Owners Thread
Although if you are using a 2017 or later LG Oled their Dynamic Tone Mapping feature has similar effect.
While some seem to have had issues with X700, mine has been problem free. I bought it for DV before the UB820 had the DV firmware update (and after I sent back my first UB820 due to player noise). For DV the X700 and UB820 PQ are about the same. The UB820 wins out for HDR10 UHDs on my LG E8 due to the Optimiser and picture adjustment controls.
If you want a Panasonic player and can't stretch for the UB820 price the UB450 may offer the best all round solution if DV playback is a big thing for you. I've noticed that many recent UHDs are being mastered at <1000 nits levels where the Optimiser wouldn't be working anyway if you've set up display type as Oled (1,000 nits).
Hence the commonly seen complaint that HDR Optimiser isn't working as people can't see a difference between it on or off (there isn't one for lower nit level discs as it's functions are off for them despite it showing as being on). One nice feature unique to the UB820/UB900 is that it shows the disc mastering and metadata info and the changes that Optimiser is doing in a pre/post display panel.
The main benefit I found for Optimiser was with some earlier UHDs (mainly Sony 4K 35mm film scans) like Crouching Tiger, Max Max and Starship Troupers which were mastered at 10,000 nits and where my LG E6 really struggled to tone map them properly. My E8 does a bit better job with them but Optimiser and picture adjustment controls are essential to tone down enhanced grain levels and way too high contrast. LG Oled 2017 models onwards Dynamic Tone Mapping feature can do similar but without the user selectable tweaks that UB420/UB820 offer (although I see that LG are now offering user selectable tone mapping options so depends if you have a x9 or are considering say a LG CX in the future).
Before recent discs being mastered at <1000 nits I would have said I find Optimiser/picture adjustment controls more useful as it works with the majority of my UHDs. Now that many UHDs are being mastered at lower nit levels it doesn't have as much benefit although I still tweak them with UB820 System Gamma and Tone Curve (black) controls.
If you don't use your UB900 picture adjustment controls much you'll likely also do similar with UB820 so the UB450 not having them won't be much of a loss. If you do use them, not having them available may be an annoyance over time. In that situation I'd try and stretch for a UB820. Otherwise if DV playback at the cheapest cost is your priority UB450 may suit (or Sony X700).