AI...good in theory, impossible to do well in your situation. A bull will ALWAYS be smarter than you about when a heiffer is in standing heat and get the job done faster. Get a bull..cheaper by far in long run. Get bull, fertility test, keep 3 to 4 months, sell bull along with any that you did not observe him breeding because they are not cycling.
With AI, compute costs of:
equipment
classes for you to do it
a chute to do it in
time spent in heat observation, rounding up within 4 hr period, 24/7
figure at very, very best a 50% success each time
figure opportunity cost in months for each failure attempt
personal injuries from handling so many heifers so close and so frequently given your experience and pens
I could go on, but if this doesn't convince you, it'll be an educational experience.
Net is, you won't break even for several years...it's very hard even for large experienced operators who are already all set up. Heifers are the most expensive part of a cow operation...you buy by the lb and sell by the lb...either the heifer or the calf. Weight added has to come from grass and or feed which costs less than it takes to put that lb on. Cheap feed does not come in a bag, bulk feed requires storage facilities and vermin control. Vet bills are greatest on first calf heifers also death loss for calves and heifers. For that sized herd, figure 1 dead heifer, 2 dead calves. A dead animal has a distressingly slow growth rate! The weight you bought, fed and lost has to be offset by the remaining animals growth before you break even.
IMHO, the best strategy is for you to gain experience, grow them up and sell before winter comes and leave the breeding and feeding to the next owner.
If I keep these calves and breed them I would rather AI than have a bull I think. What are the advantages of AI, cost etc.?