Yeah he needs to tell what kind of performance hes trying to get before we can really suggest anything, old xeons are not a joke still if you find a good deal.
1. Lynnfield cpu (Nehalem architechture 1st gen intel) or Socket 1156. These offer up to 4 core 8 thread processsors like i7-870 or for example cheaper options which still work and are overclockable like x3440 or x3470. With these you need to get from 2.5-2.9ghz to atleast 4.0ghz to get "decent" performance for 1080p. These are still the best cpu for value you can find anywhere, x3440 is about 8 dollars including shipping worldwide from aliexpress, however x3440 is locked to 19x multiplier which makes overclocking harder and you need to hit way higher BLCK to reach 4ghz or over, X3470 has more overclocking abilities since you can go higher multiplier but its way more expensive ( 25$ shipped). For a motherboard i suggest used Asus P7P55D or its variants, this will get you well over 4ghz with good power supply. There are other good motherboards aswell but these are most available.
Maximum suggested GPU (if your running stock speed on cpu) gtx 960 / 970 or 1050ti. Overclocked to 4.2ghz you can max out gtx 1060, gtx 980 and 1660. Total price for motherboard + cpu + ram would be about 50-60euros or dollars.
2. Westmere xeons X58 (
LGA 1366 socket) platform, these are slightly newer processors but still ancient, good deal would be something like x5675 processor (6 cores 12 threads) with asus p6x58d-e motherboard. You can reach even 4.4-4.6ghz on these with good cooling. Processor prices from 10 to 40$ shipped. Motherboards can be quite expensive even used. I got decent deal on x5675 + asus p6x58d-e and 3x4gb ddr3 1866mhz ram for 100 euros total. Chipset supports triple channel ram , so best way is to run 3 ram sticks instead of 2 or 4 like in dual channel. There are many other good processors for LGA 1366 you need to read into it, overclocking can be more time consuming on these, max multipliers and clock speed will wary depeninding on the processor you pick. Maximum GPU suggested i would say your fine with 980ti, 1070 / 1070ti , 2060. Maybe even 2060 super if you get cpu running 4.5ghz.
A good deal would be around 100 dollar / euro for ram+motherboard+cpu.
3. Ivy bridge x79 , Everything until this point was really cheap but if you decide to go with this platform instead of E5-1620 v2 which is 4 core 8 thread processor you should be looking more into E5-1650 v2 (this has 6 core 12 threads ) or even E5-1680 v2 (8 core 16 threads) since performance increase is huge, these all are FULLY overclockable. You can look differences here :
https://www.cpu-world.com/CPUs/Xeon/Intel-Xeon E5-1680 v2.html , But E5-2000- series cpu:s are not fully unlockable , you can only unlock turbo which is NOT all cores, i suggest going for E5-16** cpu, ONLY versions v1-3 , the v4 is LOCKED. So E5-1600 series with V1 V2 or V3 if you plan on buying one of these. An E5-1650 v2 overclocked to 4.5 or 4.6ghz is same as i9-9900k running on stock speeds performance wise.
For GPU recommendation you can pretty much max out everything but some of the 3000 series cards or 2080ti with this one, depending if you overclock (just compare to i9-9900k stock).
Good youtube which compares x79 to newer cpu:s :
View: https://www.youtube.com/watch?v=xYxQ82wcA_s