You can make your mountain bike a little more tri friendly by modifying the your bike. Tire change. Lighter fork… The expense would be minimal compared to a new road bike for you right now. We did this with my son’s bike a what a difference!
Oh wow!! I had no idea you could do this!! I’ll have to ask at the shop about that…but my bike is also getting very old, so I’m not totally sure it would be worth the expense. But it is definitely worth asking about!