The Tika t3 can be had for $500 new. The ones I've handled have been decent rifles just aren't my cup of tea. The only Nikon scope I've used has been a monarch 1.5-6x, it's been a good one for me. That particular model I can't give you any info on but they have stopped making scopes and if you had an issue warranty work might be a problem.
Stepping up from 243win to 25-06 won't make too much difference on deer unless you've got really big deer or plan on shooting past say 400yd regularly. I've got both and while my 06 slinging 110 and 115gr bullets seem to hit like lightning. That being said 243 slinging 95gr Hornady SST in my rifle, or 80gr Speer hot-core in my pistol kills them just as dead. Inside 200yd I've had lots of bang flops on 90-130lb doe. My biggest buck to date was killed when I was 16 with my little 243 "woman's gun" 100gr bullet wrecked his heart and lungs and stopped under the hide on his offside, he only ran 40yd. Don't let anyone tell you 243 isn't a good deer gun, shot placement is the key with any critter bigger than a groundhog. If you get surgical with that rifle the "little" 6mm bullets will kill anything you care to hunt. I've personally dropped more deer with that caliber than my buddies shooting much bigger guns.
I feel you're better off upgrading glass on your 243, can never go wrong buying the better glass. Not enough difference in performance that I've seen jumping up if you've already got a deer rifle.
If you want a laser of a varmint round look at the 58gr 243 loads they'll run around 4000fps. You can get the varmint gun performance for spring and summer and sight back in with 95-100gr loads for deer.