Honestly no point in upgrading your cpu really, you're not going to get much performance gain staying in anything that supports ddr3 unless you go down the x79 and an old xeon, but I wouldn't recommend it.
A b450 with a ryzen 5 3600 and 16gb of ram can be had for around £300 which if you sold your ram and CPU and added that to your 150 budget it wouldn't leave you much short, it's just not worth spending 150 on 9 year old hardware.
The best B450s are the msi tomahawk, mortar and pro carbon which are even capable of running 16 cores CPUs. A cheaper option would be the asrock pro4.
I have an overclocked 2700K still, no plans to replace it yet. It sits at 5GHz normally (4.6GHz in this hot weather) and it still does the job fine playing games in 4K etc.