These are extremely different. Full frame vs APS-C, full DSLR vs mirrorless. A 5D with the glass to go with it is a much larger investment, more $$ now, more moving forward, more weight.
Doesn't have to be more expensive. Tons of OK FF glass is out there, especially on the used market. Canon now has the new 24-105 f3.5-5.6 IS, but on the used market you can choose between the IS 28-135 f3.5-5.6 or the non-IS 24-85 f3.5-4.5 and 28-105 f3.5-4.5. Despite their age DXO rates them sharper than current kitlenses and they can all be picked up for 100-200$ and all have USM AF.
There are also many great primes that don't break the bank like Canon's excellent 35mm f2 and 85 and 100mm f1.8. With the cheap 50mm f1.8 you also get the 'full frame'.